1. society
2. work
3. unemployment

PERUVIAN ECONOMIC ASSOCIATION
Worker Mobility in a Search Model with Adverse
Selection
Carlos Carrillo-Tudela
Leo Kaas
Working Paper No. 40, April 2015
The views expressed in this working paper are those of the author(s) and not those of the Peruvian
Economic Association. The association itself takes no institutional policy positions.
Worker Mobility in a Search Model
with Adverse Selection ∗
Carlos Carrillo-Tudela
†
Leo Kaas
‡
February 12, 2015
Abstract
We analyze the effects of adverse selection on worker turnover and wage dynamics in
a frictional labor market. We consider a model of on-the-job search where firms offer
promotion wage contracts to workers of different ability, which is unknown to firms at the
hiring stage. With sufficiently strong information frictions, low-wage firms offer separating
contracts and hire all types of workers in equilibrium, whereas high-wage firms offer pooling
contracts, promoting high-ability workers only. Low-ability workers have higher turnover
rates and are more often employed in low-wage firms. The model replicates the negative
relationship between job-to-job transitions and wages observed in the U.S. labor market.
Keywords: Adverse Selection, On-the-job search, Worker mobility, Wage dynamics.
JEL: D82; J63; J64
∗
The paper is a substantially revised and developed version of our earlier working paper “Wage dispersion
and labor turnover with adverse selection” (Carrillo-Tudela and Kaas (2011)). We would like to thank the
Associate Editor, two referees, Jim Albrecht, Melvyn Coles, Javier Fernandez-Blanco, Miltos Makris, Espen
Moen, Peter Norman, Fabien Postel-Vinay, Ludo Visschers and Susan Vroman for their comments and insights.
We especially thank our research assistant Vigile Fabella for her contributions. We also thank participants at the
“Essex Economics and Music” workshop 2011, SAET 2011, SED 2011, the “Matching, Theory and Estimation”
conference at Science Po 2013, and at seminars in BI Oslo, Mainz and Carlos III. The usual disclaimer applies.
†
Corresponding author: Department of Economics, University of Essex, Wivenhoe Park, Colchester, CO4
3SQ, UK. Tel: +44(0)1206873414. Email: [email protected]
‡
Department of Economics, University of Konstanz, 78457 Konstanz, Germany.
Email:
[email protected]
1
1
Introduction
1.1
Motivation and Summary
The ability of the labor market to allocate resources hinges upon the type and severity of the
frictions that prevent workers and firms in forming the most efficient matches. On the one hand,
theories of search frictions emphasize the costs associated with finding the right worker or the
right job. Theories of adverse selection, on the other hand, stress the importance of asymmetric
information at the hiring stage as an impediment for labor turnover.1 Taken together these
frictions can present formidable barriers for worker turnover and efficient resource allocation.
Lockwood (1991), for example, suggests that adverse selection exacerbates the negative effects
of search frictions by reducing the re-employment chances of unemployed workers. With almost
no exceptions, however, current contributions on labor search with adverse selection abstract
from job-to-job flows,2 although these transitions account for a sizeable part of worker flows.
Furthermore, the rate at which workers change jobs is an important determinant of wage dynamics (see, e.g., Topel and Ward (1992)). Thus one would expect that asymmetric information
not only has non-trivial implications for workers’ job turnover, but also for how their wages
evolve over time.
In this paper we present a theoretical analysis of the interaction between search frictions,
on-the-job search and asymmetric information. Our objective is to study how asymmetric information about workers’ abilities affects the mobility of workers within and across firms in a
frictional labor market. A key implication of our model is that high-wage firms offer more attractive employment conditions to high-ability workers than to low-ability workers. This implies
that low-ability workers have higher turnover rates even though all workers face the same degree
of search frictions.3 We show that our model is quantitatively consistent with the observed negative relationship between wages and the number of job-to-job transitions we uncover using the
National Longitudinal Survey of Youth (NLSY). In particular, workers that undertake substantial job changes have on average lower earnings than workers who change relatively fewer times.
This is in contrast with standard theories of on-the-job search such as Burdett and Mortensen
(1998), which we show predict a positive relationship between wages and the number of job-tojob transitions. We further show that the negative relationship between those variables observed
in the data is generated by worker unobserved heterogeneity, as implied by our model.
We consider a frictional labor market similar to Burdett and Mortensen (1998), where workers search randomly for job opportunities and firms commit to long-term wage contracts. In
deviation from this benchmark, information is asymmetrically distributed in our model: while
workers are perfectly informed about their ability, firms learn workers’ ability slowly over time.
1
Search models of the labor market are surveyed in Rogerson et al. (2005). For labor market implications of
adverse selection, see e.g. Salop and Salop (1976), Greenwald (1986), Gibbons and Katz (1991).
2
We review some of this literature in Section 1.2 below.
3
The empirical findings of Kahn (2013) indeed suggest that workers with higher job mobility patterns are on
average of lower ability than those who move relatively less.
2
Further, firms post a menu of promotion contracts, one for each worker type, to which they are
committed. Any contract offers an initial wage based on the worker’s reported ability. Upon
learning the worker’s type, the firm promotes the worker if the worker reported his type truthfully; otherwise the worker is demoted.
When a meeting takes place, the worker chooses whether to accept the job and the terms
of employment based on the reported ability. By misreporting his type, a low-ability worker
earns a higher initial wage but faces the possibility of demotion accompanied by a wage cut.
By reporting truthfully, the worker earns a lower starting wage but faces the prospects of a
promotion with a wage rise. This trade-off determines the incentive-compatibility constraint
that firms must satisfy if they want to separate workers at the hiring stage. A key result is that
the firms’ willingness to separate their applicants depends on the degree of information frictions
relative to search frictions. Indeed, adverse selection adds a novel trade-off in the firm’s problem.
By offering high initial wages to attract and retain more high-ability workers, it becomes more
costly to satisfy incentive compatibility so as to separate workers. As information frictions
increase relative to search frictions, these separation costs become larger. Stronger information
frictions (or lower search frictions) imply that workers have a higher chance of moving to another
job before the firm learns their type, making it even more attractive for workers to misreport
and more difficult for firms to separate at the hiring stage.
In equilibrium, firms follow one of two strategies. Either they decide to offer separating
contracts or they offer pooling contracts. Firms offering pooling contracts hire all workers at the
same initial wage, promoting high-ability workers and demoting low-ability workers after their
types are revealed. Firms offering separating contracts hire workers at different initial wages
and promote all workers who self-select into the right contracts. The offer distribution of initial
wages for each ability type is always dispersed for similar reasons as in Burdett and Mortensen
(1998). We find a cutoff value of the firms’ learning rate such that when firms learn sufficiently
fast, a separating equilibrium emerges where all firms offer separating contracts. Otherwise,
there exists a segmented equilibrium in which low-wage firms offer separating contracts while
high-wage firms offer pooling contracts. The segmented equilibrium has particularly interesting
qualitative properties: because high-wage firms demote workers of low-ability, these workers have
higher turnover rates than high-ability workers. Hence, they are more frequently employed in
low-wage firms who then end up with a less productive workforce.4 The segmented equilibrium
also features rich individual wage dynamics, including wage cuts and wage gains, both within
and between firms.
To analyze the quantitative implications, we calibrate our model to match the monthly rates
and the wage gains/losses associated with job-to-job transitions, job-to-nonemployment transi4
Idson and Oi (1999) suggest that smaller firms are less productive because they attract and retain less
productive workers than larger firms. They argue that this is due to complementarities between capital and
labor, while they are silent on the way recruitment and retention policies firms use to achieve a more productive
workforce. Our theory provides a possible explanation. See Lentz (2010) for a model in which high-ability workers
search harder and hence have a higher chance of being employed in high-wage firms.
3
tions and within-firm promotions, as observed in the U.S. for workers with ten years of potential
work experience. Our estimate for the firm’s learning rate follows Lange (2007). The segmented
equilibrium that arises in the calibration has novel features relative to standard labor search
models without information frictions, such as Burdett and Mortensen (1998). In the calibrated
model, for example, larger firms have higher internal mobility, pay higher wages, employ a more
productive workforce and exhibit less separations (see Idson (1989) and Papageorgiou (2014),
among others).
The main implication of our calibrated model pertains to the relationship between the cumulative count of workers’ job-to-job transitions and (log) wages. We show using NSLY data
that an OLS regression generates a negative relationship between these two variables, after
controlling for a large set of observable characteristics including the cumulative count of nonemployment spells.5 Our calibrated model generates this negative relationship, while a Burdett
and Mortensen (1998) model predicts a positive relationship.
We further analyze whether worker unobserved heterogeneity might be driving the negative
relationship between the number of job-to-job transitions and wages observed in the data. This
exercise is important as our model predicts that this should be the case. To test this prediction
we control for possible correlations between a time-invariant worker effect in the error term and
the cumulative count of job-to-job transitions. Once we control for such a correlation, we find a
positive relationship between the cumulative count of job-to-job transitions and wages. Hence,
standard job ladder models seem to be fully consistent with the data once we account for worker
unobserved heterogeneity. However, those models miss the fact that some workers churn a lot
in the labor market and yet remain largely unsuccessful.
The rest of the paper is organized as follows. After a brief review of the related literature, we
set out the basic framework in Section 2. In Section 3 we characterize separating and segmented
equilibria. Particularly, we show that all firms separate their applicants when the firms’ learning
rate is high enough; but when information frictions are sufficiently severe, a fraction of high-wage
firms offer pooling contracts and end up retaining more high-ability workers. In Section 4 we
calibrate our model and explore its implications for worker turnover and wage dynamics. Section
5 discusses alternative learning processes and analyzes an extension where firms can condition
their contracts on workers’ employment status. In the latter case, we show that employment
status gives firms further monopsony power, which in turn makes it easier to separate workers
at the hiring stage. Section 6 concludes. All proofs, tedious derivations and data analysis are
relegated to the Appendix.
1.2
Related Literature
In their recent survey paper about hiring and incentives, Oyer and Schaefer (2011) call for
further theoretical exploration about the effects of asymmetric information at the hiring stage
5
This is inline with previous empirical studies that find that more job turnover is associated with lower average
wages (see, e.g., Mincer and Jovanovic (1981) and Light and McGarry (1998)).
4
in a frictional labor market. We contribute to this literature by developing an equilibrium
model of random search in which firms commit to self-selecting contracts to study the effects
on worker turnover and wage dynamics. We allow firms to face the risk of losing workers to
other firms through competition brought about by workers’ on-the-job search. In general, firms
may also use other screening devices like aptitude tests, but those can be costly to implement
or might not reveal the desired information. Salop and Salop (1976), for example, show how
firms can use deferred compensation contracts to separate workers with high and low quit rates.
Lazear (2000) and Oyer and Schaefer (2005) emphasize the importance of self-selection contracts
in explaining the use of performance-based pay in organizations. Here we explore the role of
promotion/demotion contracts as a self-selection device that helps firms to separate applicants
at the hiring stage.
Besides a few earlier contributions (e.g. Lockwood (1991), Albrecht and Vroman (1992),
Montgomery (1999)), a number of more recent papers study the interrelation between search
frictions and adverse selection. Guerrieri et al. (2010) analyze existence and efficiency properties
of competitive search models with adverse selection, characterizing separating equilibria where
different worker types are employed in different contracts. As they consider a static environment,
they cannot discuss worker turnover or wage dynamics. Inderst (2005) analyzes existence of
separating equilibria in a model of random search with adverse selection. In his model, the
composition of the pool of searching individuals evolves over time. However, once a productive
match is formed and a contract agreed, the pair leaves the market. To the best of our knowledge,
there are only two papers with on-the-job search under adverse selection. Kugler and Saint-Paul
(2004) analyze the effects of firing cost on different types of workers in a model with search
on-the-job, assuming however an ad-hoc wage schedule. This is very different from this paper
which is interested in optimal wage policies under adverse selection. Visschers (2007) considers
a model with random search based on Stevens (2004) and assumes that both the worker and
the employer do not observe the worker’s (match-specific) ability at the start of the relation.
Although the employer learns faster than the worker, it offers the same wage contract to all its
new hires.
A few papers consider the interaction of search frictions and adverse selection to study firms’
decisions to offer a take-it-or-leave-it wage offer or to engage in bilateral bargaining with their
job applicants. Camera and Delacroix (2004), for example, consider a random search model,
while Michelacci and Suarez (2006) consider a directed search model to address this issue. As
in our paper, firms choose between different contracts which impacts the type of workers they
employ. Michelacci and Suarez (2006) show that the labor market segments and firms posting
wages attract workers with low productivity, while firms that bargain attract high productivity
workers. In our paper we restrict attention to wage posting and we let firms choose between
offering separating contracts to hire both types of workers at different wages or posting a pooling
contract that provides a higher retention rate for high-ability workers.
This paper also relate to the literature that studies employer learning to analyze worker
reallocation. Jovanovic (1979), Moscarini (2005) and Papageorgiou (2014) provide insightful
5
examples. This literature typically focuses on bilateral asymmetric information where the firm
and the worker jointly observe signals about the match quality over time. An important empirical
literature has developed from such insights, aiming to test the degree of asymmetric information
and the speed of employer learning (e.g. Altonji and Pierret (1996), Lange (2007) and Kahn
(2013)). These papers imply that low-ability or poorly matched workers are negatively selected,
facing a higher turnover rate. Our paper constructs a tractable equilibrium wage-posting model
with adverse selection, on-the-job search and firm learning. In this setting we analyze how
the degree of frictions in the labor market and firms’ speed of learning affect their hiring and
retention strategies. We show that the resulting workers’ job mobility and wage patterns are
quantitatively consistent with evidence for the U.S. labor market.
2
Basic Framework
2.1
Workers and Firms
Consider the steady state of a continuous time economy which comprises a continuum of workers
and a continuum of firms. The life of any worker has uncertain duration and follows an exponential distribution with parameter φ > 0. To keep the population of workers constant, φ also
describes the rate at which new workers enter the labor market. Firms are infinitely lived. All
agents have a zero rate of time preference and are risk neutral. The objective of any worker is
to maximize total expected lifetime income, and the objective of any firm is to maximize the
expected steady-state profit flow.
There are two types of workers who differ in their innate ability. A mass αH = 1 of workers has
high ability pH and a mass αL = α has low ability pL . All firms operate the same constant returns
to scale technology, producing flow output pi with every employed worker of type i = H, L. While
workers are perfectly informed about their type upon entering the labor market, the firm does
not know a worker’s ability at the hiring stage. We assume that firms monitor the output of a
particular worker at exogenous rate ρ, which describes the firm’s learning rate.6 Once the firm
has learned the worker’s ability, the latter can be verified in a court of law.
In other respects the information structure mirrors that of the Burdett and Mortensen (1998)
model. In particular, firms cannot make offers contingent on the applicants’ employment histories. As it will become clear later, this assumption is important since a firm could use information
on its applicants’ current wages or their wage histories to update its beliefs.7 However, allowing
offers to be contingent on these characteristics also involves dealing with the worker’s decision
6
The implicit assumption here is that the firm observes total output, but since it employs a mass of workers
it is too costly to observe the output of each individual worker immediately. In Section 5.2 we further discuss
the firms’ learning process.
7
In Section 5.1 we discuss a variation of the model in which firms condition their contracts on workers’
employment status and analyze whether this information makes it easier for firms to separate workers.
6
of whether to reveal this information truthfully to the firm. In principle workers would be unwilling to do so since the firm would then be able to condition its contract on workers’ current
reservation wages, individualizing their offers, and extracting further rents. We do not pursue
this possibility here as it would complicate our analysis even further, raising difficult signalling
issues at the recruitment stage. Instead we assume that firms must treat equally all applicants
that report a given type.
Unemployed and employed workers meet firms according to a Poisson process with parameter
λ > 0. There are also job destruction shocks in that each employed worker is displaced into
unemployment according to a Poisson process with parameter δ > 0. Once unemployed, any
worker receives a payoff of b < pL per unit of time. For simplicity we do not allow that workers of
different abilities obtain different payoffs when unemployed. The flow payoff b can be interpreted
as flow income from unemployment benefits (imposing equal treatment across workers) or as flow
utility from leisure (imposing identical leisure preferences).
2.2
Contracts
We consider flat–wage contracts that allow for promotions or demotions when the firm verifies the
worker’s type. All other transfers between workers and firms (at the hiring stage or thereafter)
are ruled out. That is, a contract contains a commitment to three wages: the initial wage (paid
prior to learning), a promotion wage and a demotion wage. When a firm meets a worker, the
firm offers a menu of two contracts, indexed by the worker’s reported ability i = H, L. We
denote these contracts as ωi = (wi , wi+ , wi− ) where wi denotes the initial wage that is paid in
the probation period, i.e. before learning the worker’s type. When worker i reports his ability
truthfully, he is promoted to receive the promotion wage wi+ as long as he stays employed in
the firm. If worker j 6= i misreported his type in contract ωi , the worker is demoted in which
case the worker is paid the demotion wage wi− for as long as he stays employed in the firm. The
firm commits to pay the initial wage wi until the worker’s type is revealed and to follow the
promotion/demotion commitment thereafter.8 While firms commit to wage profiles, they cannot
commit to retain workers that yield negative expected profit value.9
Upon meeting the firm, the worker observes the posted contracts and can choose one of them,
but nothing restricts the worker from choosing the contract the firm designs for workers of a
different ability level. If both contracts are rejected, however, the worker remains in his current
state with no option to recall previously met firms. We make the following tie-breaking assumptions: an unemployed worker accepts a wage offer if indifferent to accepting it or remaining
unemployed, while an employed worker quits only if the offer is strictly preferred.
8
In a previous working paper version (Carrillo-Tudela and Kaas (2011)), we consider a contractual environment
in which firms are restricted to offer flat wage contracts without promotions, but can threaten to fire workers
who misreport their type upon learning. We also consider contracts allowing wage cuts for misreporting workers.
9
The underlying assumption here is that both the worker and the firm are free to initiate a separation at any
time. But even if firms were able to commit to employ unprofitable workers, our main segmentation results would
survive; see also footnote 18 below.
7
To summarize, the main restrictions we impose on the contract space are: (i) equal treatment at the hiring stage to all workers that report a given type; (ii) flat-wage contracts where
promotions and demotions occur together with learning events; and (iii) no side payments.
2.3
Equilibrium
When a worker of type i = H, L encounters a new employer offering contract menu [ωH , ωL ] =
+
−
[(wH , wH
, wH
), (wL , wL+ , wL− )], the worker may report his type truthfully, which leads to continuation utility Vii (ωi ), or the worker may misreport his type with continuation utility Vij (ωj ) for
i 6= j. The flow gain from misreporting the type is the difference in initial wages, wj − wi . After
the firm learns the worker’s type, the worker either receives continuation utility Vi (wi+ ), if he
reported his true type, or Vi (wj− ), if the worker misreported his type. Since learning occurs at
Poisson rate ρ, worker i’s incentive constraint Vii (ωi ) ≥ Vij (ωj ) is equivalent to
wj − wi ≤ ρ[Vi (wi+ ) − Vi (wj− )] .
(1)
This incentive constraint describes the main trade-off faced by a worker when meeting a firm.
By misreporting his type, worker i earns potentially the higher initial wage wj but faces the
possibility of demotion with continuation utility Vi (wj− ). By reporting truthfully, the worker
possibly earns a lower starting wage but faces the prospects of a promotion, yielding continuation
utility Vi (wi+ ). The worker will report his type truthfully and self-select into the right contract
when the flow gain from misreporting does not exceed the expected gain from a promotion
relative to a demotion.10 In Appendix A we present the recursive equations for Vii , Vij and Vi
and derive this incentive constraint formally. We write Ui for the utility value of unemployment
for a type-i worker.
Firms choose contract pairs (ωH , ωL ) to maximize the steady-state profit value ΩH (ωH ) +
ΩL (ωL ), where Ωi (.) denotes the firm’s profit from hires in contract ωi . Firms take into account
that workers may misreport their type whenever the incentive constraint (1) fails in which case
the firm pools all workers in the same contract. In such cases, the profit value Ωi (ωi ) also includes
the gains (or losses) from workers of type j who are later demoted to wage wi− .
A market equilibrium is a joint distribution Ψ of contract offers, and value functions Ui , Vi ,
Vii , Vij , Ωi , i, j = H, L, for workers and firms such that (i) every (ωH , ωL ) in the support of Ψ
maximizes firms’ profits subject to optimal turnover and truth-telling behavior of workers; and
(ii) workers’ turnover and reporting strategies are optimal given that new contract offers are
drawn randomly from distribution Ψ at Poisson rate λ.
In the following subsection, we consider those market equilibria where the promotion and demotion wages are maximally differentiated so that the incentives to report truthfully are as large
as possible, given the constraint that workers and firms may voluntarily quit any employment
10
Note that this trade-off is similar to the one found in efficiency wage models, in which shirking (misreporting)
yields a higher utility (initial wage) but implies a higher probability of being caught and fired (demoted).
8
relationship. These constraints imply in particular that wi+ ≤ pi (otherwise a firm would fire
the worker) and wi− ≥ b (otherwise the worker would quit to unemployment). In spite of strong
incentives, however, a market equilibrium does not always give rise to a perfect separation of
workers. In fact, as we show in Section 3, some firms may decide to pool all workers in the same
contract, so that low-ability workers are demoted in equilibrium. Those workers then experience
higher turnover rates as well as upward and downward wage mobility, both within and between
firms.
2.4
Equilibrium Restriction
In the following we restrict the analysis to those market equilibria where all firms offer contracts
of the form ωi = (wi , pi , b), which we label simple contracts. That is, firms demote misreporting
workers by cutting their pay to the reservation wage,11 while they promote truth-telling workers
to their marginal product. This maximally feasible differential between promotion and demotion
wages provides the greatest possible incentives for workers to report their type truthfully upon
hiring. Further, backloading of wages for truth-telling workers serves the purpose of minimizing
turnover while earning positive profits on lower initial wages prior to learning.
In Section 3, we characterize all candidate equilibria where firms are restricted to choose
simple contracts. Before we do that, however, we show in the following lemma that those
candidate equilibria are indeed market equilibria (where firms are allowed to choose arbitrary
contracts (wi , wi+ , wi− )). This result holds generally when all firms offer separating contracts.
In those cases where some firms pool workers, a specific parameter restriction is required to
guarantee that the candidate equilibrium in simple contracts is indeed a market equilibrium.
For the plausibly calibrated parameter combinations that we consider in Section 4, we verify
that this condition is satisfied so that the considered promotion/demotion strategies are in fact
equilibrium outcomes.12 For a given candidate equilibrium in simple contracts, we write Fi for
the marginal distribution of starting wage offers to workers of type i. Further, let Ri denote
the reservation starting wage for an unemployed worker of type i who reports truthfully when
meeting a firm. This reservation starting wage is smaller than unemployment income b, since
truth-telling workers can expect a promotion to wage pi > b with positive probability. In
Appendix A we show that all workers indeed follow a standard reservation-wage strategy.
Lemma 1: Consider a candidate equilibrium in simple contracts where Fi is the marginal
distribution of wage offers to workers of type i and Ri is worker i’s reservation starting wage,
i.e. Vii (Ri , pi , b) = Ui . Then the candidate equilibrium is a market equilibrium if all firms offer separating contracts. If some firms pool all workers in the same contract, the candidate
11
Since the offer arrival rate is independent of a worker’s employment status, b is the common reservation wage
for both worker types.
12
If the parameter condition fails, pooling firms would offer dispersed demotion wages which considerably
complicates the equilibrium analysis without providing additional economic insights. We therefore only consider
equilibria in simple contracts which already give rise to rich wage dynamics between and across firms.
9
equilibrium is a market equilibrium if the condition Γ(w) ≤ Γ(RL ) holds for all w ∈ [RL , pL ],
where
R w φ+δ+λ(1−FL (w0 ))
0
pL − b − RL φ+δ+ρ+λ(1−F
0 dw
L (w ))
Γ(w) ≡
.
φ + δ + λ(1 − FL (w))
The condition Γ(w) ≤ Γ(RL ) is needed to ensure that the demotion wage wL− = b is indeed
optimal for all pooling firms. For equilibria in simple contracts, we further obtain a convenient
formulation of the incentive constraint, stated as follows.
Lemma 2: In any equilibrium in simple contracts, the incentive constraint for type i workers
is
wj − wi ≤ b − Ri .
3
(2)
Equilibrium Analysis
3.1
Preliminary Considerations
Before we analyze the different equilibria in simple contracts, we discuss a few general properties.
A first insight is that firms offer contracts with dispersed starting wages which gives rise to worker
turnover before the promotion/demotion events. That is, the distributions Fi of starting wages
are non-degenerate. Workers employed at starting wages quit to other contracts if and only if
they provide strictly higher continuation value. The reason for contracts with dispersed starting
wages is that promotions and demotions are linked one-to-one to employer learning which is a
stochastic event. Since promotion dates are uncertain, workers quit to contracts offering higher
starting wages during the probation period. Firms, in turn, respond to these incentives by offering
dispersed contracts, trading off higher flow profits against higher attraction and retention rates,
+
similar to Burdett and Mortensen (1998).13 Promoted workers of type H (earning wH
= pH )
never quit since no firm can offer a greater continuation value. However, there can still be
turnover of low-ability workers after they have been promoted or demoted, as we see below.
We restrict the analysis to rank-preserving wage policies: firms that offer higher starting
wages to high-ability workers also offer higher starting wages to low-ability workers; that is,
there is an increasing function w(.)
b such that FL (w(w
ˆ H )) = FH (wH ) for all wages wH in the
support of the offer distribution FH . If any of the incentive constraints (2) binds (on some
interval), rank preservation follows directly because wL increases one-for-one with wH (no matter
which constraint binds). But if incentive constraints are slack in some range of the wage offer
13
See Stevens (2004) for the case in which firms pre-commit to a promotion date without facing the adverse
selection problem we introduce in our paper.
10
distributions, any wage offer wL in this range satisfying incentive compatibility yields the same
profit, so that wage offers across firms can be ordered in a rank-preserving way.14 Before we
proceed, note that offering initial wage wi = Ri strictly dominates offering any wi < Ri as
it generates strictly positive profit while the latter leads to zero profit. And because contract
(Ri , pi , b) attracts unemployed workers, Ri is the lower bound of the support of Fi .
It is useful to note that in any equilibrium the incentive constraint does not bind at low wages
and hence firms offering these wages will always separate workers at the hiring stage. To see this
consider the lowest contract offered in equilibrium, (RH , RL ). Condition (2) implies that when
meeting a firm offering this contract, a high-ability worker’s incentive constraint does not bind
whenever RL < b and a low-ability worker’s incentive constraint does not bind whenever RH < b.
Since Ri < b for i = L, H, the previous conditions are always satisfied. Rank preservation then
implies slack incentive constraints in the neighborhood of (RH , RL ).
A similar argument shows that incentive constraints do not bind for high-ability workers. For
these workers, (2) is given by wL − wH = w(w
ˆ H ) − wH ≤ b − RH . As we show in the proofs
of Propositions 1 and 2, the slope of function wˆ does not exceed one, hence the left-hand side
is weakly decreasing in wH , so that the incentive constraint holds for all wages in the support
of the wage offer distribution if it is satisfied at wH = RH . The latter condition amounts to
w(R
ˆ H ) = RL ≤ b, which is always satisfied.
Lastly, note that the arguments of Burdett and Mortensen (1998) imply that the offer distribution FH is continuous and has connected support when firms are able to separate workers.
When some firms offer pooling contracts, however, we will see that FH exhibits a mass point in
the range of wages in which firms offer pooling contracts.
We now proceed to fully characterize the equilibria in simple contracts that can arise in
this model. First we consider equilibria where the contracts offered by all firms are incentive
compatible. In those situations, which requires the learning rate ρ to be sufficiently large, all
firms promote workers who stay long enough with the firm, and they never exercise a demotion
option. In contrast, if the learning rate is sufficiently low, the market equilibrium is segmented,
featuring some pooling contracts at the top of the wage offer distribution, with promotions of
high-ability workers and demotions of low-ability workers. To save notation, we write instead of
the contract pair (ωH , ωL ) the pair of initial wages (wH , wL ), and we also write all value function
expressions in those starting wages.
14
When incentive constraints are slack, our restriction to rank-preserving wage policies has implications for
the relationship between firm size, wages and productivity we discuss in Section 4.2. Without it, firms that
offer contracts with slack incentive constraints might not exhibit a positive relationship between wages, size and
workforce productivity.
11
3.2
Separating Equilibrium
Workers
In a candidate separating equilibrium the value functions of unemployed workers i = L, H are
given by
Z wi
Vii (w) dFi (w) .
(3)
(φ + λ)Ui = b + λ
Ri
For employed workers i = L, H in probation contracts with initial wage wi , we have
Z wi
[φ + δ + ρ + λ(1 − Fi (wi ))]Vii (wi ) = wi + δUi + ρVi (pi ) + λ
Vii (w) dFi (w) .
(4)
wi
For promoted workers we have
[φ + δ]Vi (pi ) = pi + δUi ,
since these workers never quit in a separating equilibrium.15 Note again that in equation (4)
the reservation wage of an employed workers is given by the current (initial) wage since all firms
offer the same promotion wage (for a given type). The reservation (initial) wages of unemployed
workers are given by
p − φUi
Ri = b − ρ i
<b.
(5)
φ+δ
The incentive constraint for low-ability workers is
wH − wL ≤ b − RL .
(6)
As discussed before, high-ability workers do not misreport their type so that their incentive
constraint never binds. Also incentive constraints for low-ability workers are always slack at the
lowest wage of the offer distribution. Possibly, however, incentive constraints for these workers
are binding at higher wages. We denote the critical threshold wages by w˜i such that the incentive
constraint (6) is binding for wi ≥ w˜i and slack otherwise.
Steady-State Measures
Simple steady-state considerations yield the unemployment rate for both types,
u=
(φ + δ)
,
φ+δ+λ
as well as the earnings distribution of workers employed at initial wages below or equal to wi :
Gi (wi ) =
(φ + δ)Fi (wi )
.
φ + δ + ρ + λ(1 − Fi (wi ))
15
Since all firms offer incentive-compatible contracts, low-ability workers earning pL cannot gain utility by
accepting an outside offer. This will be different when firms at the top of the offer distribution post pooling
contracts.
12
Profit Maximization
Firms’ steady-state profit flows are given by ΩH (wH ) + ΩL (wL ) where
ΩL (wL ) = `L (wL )(pL − wL )
ΩH (wH ) = `H (wH )(pH − wH ) ,
,
and `i (wi ) denotes the steady-state workforce of workers of ability i who are employed at initial
wage wi . Steady state and optimal turnover then imply that in this candidate equilibrium
`i (wi ) =
λαi [u + Gi (wi )(1 − u)]
.
φ + δ + ρ + λ(1 − Fi (wi ))
The firms’ profit is therefore given by
Ωi (wi ) =
A0 αi
λ(φ + δ + ρ + λ)(φ + δ)
.
(p
−
w
)
,
where
A
≡
i
i
0
[φ + δ + ρ + λ(1 − Fi (wi ))]2
φ+δ+λ
(7)
Profit-maximizing firms are indifferent between all contracts in the support of the wage-offer
distribution. When incentive constraints do not bind (i.e., wi < w˜i ), the constant profit condition
holds for each ability type independently. Equating Ωi (wi ) = Ωi (Ri ) yields offer distributions
with a similar functional form as in Burdett and Mortensen (1998). Namely,
"
1/2 #
(φ + δ + ρ + λ)
pi − w i
Fi (wi ) =
1−
, wi ≤ w˜i .
(8)
λ
pi − Ri
For wages above w˜i , the incentive constraint (6) binds. Substitution into the firm’s profit function
gives, for wH ≥ w˜H ,
ΩH (wH ) + ΩL (wH − b + RL ) =
A0 [pH − wH + α(pL − wH + b − RL )]
.
[φ + δ + ρ + λ(1 − FH (wH ))]2
Now the constant-profit condition ΩH (wH ) + ΩL (wH − b + RL ) = ΩH (RH ) + ΩL (RL ) yields the
wage-offer distribution
"
1/2 #
p − wH (1 + α) + α(b − RL )
(φ + δ + ρ + λ)
1−
FH (wH ) =
, wH ≥ w˜H ,
(9)
λ
p−R
where we define p ≡ pH + αpL and R ≡ RH + αRL .
Rank Preservation
Using (8) and FL (w(w
ˆ H )) = FH (wH ), we obtain that
pL − RL
wL = w(w
ˆ H ) = pL −
[pH − wH ] , wH ≤ w˜H .
pH − RH
(10)
This equation then implies that the incentive constraint (6) is fulfilled for all wages
wH ≤ w˜H ≡
b(pH − RH ) − RH (pL − RL )
.
pH − RH − pL + RL
For wages above w˜H , the binding incentive constraint defines wL = w(w
ˆ H ) = wH − b + RL .
13
(11)
Slack Incentive Constraints
If the firms’ learning rate is sufficiently large (above threshold level ρ1 defined below), the
incentive constraint is slack for all wages in the wage distribution. In this situation, the threshold
wage w˜H exceeds the upper bound wH of the distribution of initial wage offers. Using (8) and
Fi (wi ) = 1, we can solve for the upper bounds
wi = pi − C 2 (pi − Ri ) , i = L, H, where C ≡
φ+δ+ρ
.
φ+δ+ρ+λ
(12)
To find reservation wages, rewrite equations (3) and (5) to obtain
Z wi
Z wi
λ(1 − Fi (w))
φ+δ
[Vii (w) − Vii (Ri )] dFi (w) =
dw ,
ρ (Ri − b) + pi − b = λ
Ri
Ri φ + δ + ρ + λ(1 − Fi (w))
(13)
where the last equation uses partial integration and the derivative of (4). Solving the integral
using (8) yields
Ri =
(φ + δ + ρ) (φ + δ + ρ + λ)2 b − ρ[(φ + δ + ρ + λ)2 − λ2 ]pi
.
(φ + δ)(φ + δ + ρ + λ)2 + λ2 ρ
(14)
Since promotion wages for high-ability workers are higher, we have RH < RL .
From (12) and (14) we obtain the top initial wages:
w i = pi −
(φ + δ + ρ)3
[pi − b] .
(φ + δ)(φ + δ + ρ + λ)2 + λ2 ρ
(15)
Since wH − wL = wH − w(w
ˆ H ) is increasing in wH , the incentive constraint (6) is slack for all
wages if it is slack at wH . Using (14) and (15), this is true if and only if
λ2 + 2λ(φ + δ) − ρ(φ + δ + ρ)
pL − b
>
.
pH − pL
ρ(ρ + φ + δ + 2λ)
(16)
This inequality defines a unique threshold level ρ1 > 0 for the firms’ learning rate such that
incentive constraints are slack for all ρ > ρ1 .16
Binding Incentive Constraints
If ρ ≤ ρ1 , incentive constraints must be binding for some wages at the top of the wage offer
distribution so that w˜H ≤ wH . In this case we can use FH (wH ) = 1 with (9) to find
h
i
2
1
wH = 1 + α p + α(b − RL ) − C (p − R) .
(17)
−b
To verify this claim rewrite (16) as ppHL−p
[ρ(ρ + φ + δ + 2λ)] = λ2 + 2λ(φ + δ) − ρ(φ + δ + ρ). Note that the
L
LHS of this equation equals zero at ρ = 0 and is strictly increasing in ρ, while the RHS is positive at ρ = 0 and
is strictly decreasing in ρ. Continuity implies that there exists a unique ρ1 > 0 that solves this equation, such
that incentive constraints are slack for all ρ > ρ1 .
16
14
Reservation wages for the two worker types are again obtained from equations (13). In Appendix
B (proof of Proposition 1) we show how these equations can be solved for RL and RH . Given
these solutions, we can back out w˜i from (11), wH from (17), wL = wH − b + RL , and the
wage-offer distributions from (8) and (9). All these equilibrium objects are uniquely defined.
The candidate equilibrium characterized by these equations only constitutes an equilibrium if
the highest initial wage offered to low-ability workers wL does not exceed their marginal product
pL . If wL > pL , firms could not credibly offer such contracts to low-ability workers since they
would prefer to layoff the worker after he signed up. In fact, if the learning rate is sufficiently
low, and given a sufficiently high job-arrival rate λ, it is possible that the highest incentive
compatible wage offer to low-ability workers exceeds their marginal product. We denote ρ2 < ρ1
as the threshold value for the learning rate such that wL ≤ pL if ρ ≥ ρ2 . This threshold value is
strictly positive if the parameter condition
2
φ+δ
p H − pL >
(18)
[p − (1 + α)b]
λ+φ+δ
is satisfied, which requires the job arrival rate λ to be sufficiently large.17 Intuitively, for larger
values of λ, firms compete more fiercely for workers which drives up the highest wage offers. At
the same time, it becomes harder to separate workers because misreporting workers quit faster
to another job before they can be demoted. Furthermore, the threat of a demotion is weaker
if workers quickly find other jobs. For these reasons, it may not be feasible for firms to offer
separating contracts at the top of the wage-offer distribution when λ is relatively large.
To verify that there is no profitable deviation for firms from the characterized candidate
equilibrium, we still need to make sure that firms do not find profitable deviations to a simple
pooling contract. In Appendix B, we prove that this claim is fulfilled provided that ρ ≥ ρ2 , and
hence wL ≤ pL . By virtue of Lemma 1, the candidate equilibrium with separating firms is a
market equilibrium. Thus, we have
Proposition 1: There are threshold values ρ1 > ρ2 ≥ 0, such that for any ρ ≥ ρ2 , there exists
a unique market equilibrium in simple contracts with dispersed offers in initial wages wi drawn
from distributions Fi and support [Ri , wi ], with Ri < b and wi ≤ pi , and separation of workers
such that
(a) if ρ > ρ1 , incentive constraints are slack for all firms;
(b) if ρ ≤ ρ1 , incentive constraints are binding for firms offering wH ≥ w˜H with w˜H ≤ wH ,
while they are slack for all other firms.
Moreover, ρ2 is strictly positive if condition (18) is satisfied.
17
In the proof of Proposition 1, we establish the existence of the threshold value ρ2 . While cumbersome
analytical expressions complicate a uniqueness proof, all our numerical examples suggest a unique value ρ2 since
the defining equation is monotonic in ρ.
15
3.3
Segmented Equilibrium with Pooling at Top Wages
If ρ < ρ2 , there is no equilibrium in which all firms are able to separate workers by offering
an incentive-compatible contract menu. In such situations, firms at the top of the wage-offer
distribution decide to offer pooling contracts designed to attract and retain high-ability workers. Low-ability workers accept these contracts, anticipating that firms demote them to their
reservation wage after learning their type.
Firms at the top of the wage distribution pool workers of high and low ability in the same
∗
contract at initial wages wH > wH
≡ wˆ −1 (pL ) = pL + b − RL . Such situations occur if the
job-arrival rate is sufficiently large (inducing firms to compete more fiercely for workers) and
the learning rate is sufficiently small (so that incentive-compatible initial wages are sufficiently
close).18
∗
Whenever firms offer pooling contracts wH > wH
, they attract all workers of low-ability that
have been promoted to pL at another (lower wage) firm since these workers strictly prefer the
job with a higher initial wage even though they expect to be demoted later on. Since there
is a positive mass of such workers which yield negative expected profit value when employed
∗
∗
in a pooling contract wH > wH
, the profit value of firms offering wH
+ ε would jump down
∗
. With a mass point
discontinuously, unless the wage offer distribution has a mass point at wH
∗
of the wage offer distribution at wage wH , a positive mass of high-ability workers employed at
∗
∗
+ ε, such that in equilibrium this profitable inflow of highquit their job to outside offers wH
wH
ability workers exactly offsets the unprofitable inflow of low-ability workers.19 Furthermore, at
∗
, pL ), equilibrium requires
the mass of firms offering the incentive-compatible contract pair (wH
that a positive fraction of low-ability workers do not self-select into contract pL but instead
∗ 20
. In fact, we prove the following:
misreport high ability by choosing wH
∗
, pL ). Low-ability
Lemma 3: If ρ < ρ2 , a positive mass of firms offer contract menu (wH
workers contacted by these firms report high ability with positive probability.
In what follows we characterize an equilibrium where a positive mass of firms offer contract
18
It is important to note that pooling at top wages will still occur even if we were to allow firms to offer
low-ability workers wages above their marginal product. This arises because firms offering the highest wages to
high-ability workers will also need to offer high wages to low-ability workers in order to satisfy their incentive
constraint. Given a small enough ρ relative to λ, such a strategy becomes too costly for high-wage firms which
then prefer to hire all workers at the same initial wage, promoting high-ability workers and demoting low-ability
ones after learning their types. See Carrillo-Tudela and Kaas (2011) for the formal argument using constant wage
contracts.
19
In the Burdett and Mortensen (1998) model, mass points in the offer distribution are ruled out because higher
wage offers would lead to a profitable inflow of workers employed at the mass point. Here this inflow is needed
precisely to compensate for the losses on low-ability hires.
20
Even though the low-wage contract is incentive-compatible, low-ability workers are indifferent between the
two contracts and they may equally well accept the contract with the higher initial wage. In principle, such
deviations could also occur at lower wages with binding incentive constraints, but firms would easily prevent
∗
those by paying ε > 0 more to workers of low ability. At the contract pair (wH
, pL ), however, such counter
deviations are not possible, since firms cannot credibly offer wages above pL to workers of low ability.
16
∗
pair (wH
, pL ) such that a fraction of low-ability workers misreport their type, so that some
pooling occurs at these firms. Possibly there is also a mass of firms offering pooling contracts
∗
w H > wH
. We can equivalently interpret such a pooling contract as a menu of contract pairs
(wH , pL ) where pL is so unattractive that low-ability workers do not accept this offer but instead
report high ability with starting wage wH . Without loss of generality and to keep the notation
consistent throughout, we specify the analysis in terms of such contract pairs where initial wages
∗
are linked according to wL = w(w
ˆ H ), such that pL = w(w
ˆ H ) for wH > wH
, thus violating
incentive compatibility (6).
In a segmented equilibrium, the different types of firms can be ranked according to their wage
offers wH ∈ [RH , wH ] as follows.
1. For RH ≤ wH < w˜H , firms offer separating contracts with slack incentive constraints.
∗
2. For w˜H ≤ wH < wH
= pL + b − RL , firms offer separating contracts with binding incentive
constraints.
∗
, pL ). Low-ability workers misreport their
3. Mass η > 0 of firms offer the contract menu (wH
type with probability ξ > 0.
∗
4. Firms offering wH > wH
pool all workers in the same contract, promoting high-ability
workers and demoting low-ability workers.
The last group of firms only exists if the learning rate is sufficiently low. In fact, in our
numerical examples, we determine a threshold value of the learning rate, denoted ρ3 (< ρ2 ),
∗
if ρ < ρ3 . For ρ ∈ [ρ3 , ρ2 ), in
such that a positive mass offer pooling contracts at wH > wH
∗
contrast, the highest pooling wage is at wH . Although we do not have an existence proof for ρ3 ,
in Proposition 2 we prove the existence of a pooling equilibrium for both these cases together.
To describe the equilibrium, suppose that mass η > 0 of firms offer the contract menu
∗
and that fraction ξ of low-ability workers who are offered these contracts opt for wH
,
∗
thus pooling with high-ability workers. Denote by ϕ = FL− (pL ) = FH− (wH ) the fraction of firms
∗
offering separating contracts strictly below (wH
, pL ). When the mass point is the highest offered
wage (ρ ≥ ρ3 ), we have that ϕ + η = 1; otherwise ϕ + η < 1.
∗
(wH
, pL ),
In Appendix B (proof of Proposition 2) we characterize a candidate equilibrium in simple
contracts by a set of equations determining the vector of equilibrium objects E ≡ (ϕ, ξ, η, RL , RH )
and we also prove that such a candidate equilibrium exists. Under the conditions of Lemma 1,
the candidate equilibrium is a market equilibrium:
Proposition 2: For any ρ < ρ2 , there exists a candidate equilibrium in simple contracts
with dispersed offers in initial wages wi drawn from distributions Fi and support [Ri , wi ], with
Ri < b. The candidate equilibrium is a market equilibrium if the condition stated in Lemma 1
∗
holds. Firms with wH < wH
= pL + b − RL offer separating contracts to all workers. There is
17
∗
also a positive mass of firms offering wH ≥ wH
who pool low-ability workers in the same contract
as high-ability workers.
We briefly discuss some of the implications for labor turnover in an equilibrium with pooling at
top wages. First, low-ability workers have a higher degree of turnover. While high-ability workers
are promoted at rate ρ and subsequently leave the job at rate φ + δ, low-ability workers expect a
demotion to wage b at flow rate ρ, with subsequent quits at rate λ (in addition to separation and
labor market exit risks). Second, the segmented equilibrium features wage gains and wage cuts,
both within firms (promotions and demotions) and between firms. Particularly, demoted lowability workers are willing to quit to new employers offering promotion contracts with starting
wages below b. Third, low-ability workers are underrepresented in high-wage (pooling) firms, and
therefore high-wage firms are more productive. Conversely, firms offering separating contracts
have a higher proportion of low-ability workers in their workforces. Furthermore, since quit
∗
rates are falling in wages, the proportion of high-ability workers is increasing in wH > wH
among pooling firms. The intuition is that high-wage firms are able to attract and retain more
workers of both types, while they demote misreporting low-ability workers at the same rate ρ
(who subsequently quit at rate λ), independent of the offered initial wage.21 We summarize these
observations as follows.
Corollary 1: If ρ ≥ ρ2 , both worker types have the same turnover patterns, no worker
experiences wage cuts without intervening unemployment spells, and all firms have the same
ability composition of the workforce. If ρ < ρ2 , low-ability workers have higher turnover rates,
and they experience wage cuts within and between firms. Firms offering pooling contracts (highwage firms) have a more productive workforce than firms offering separating contracts (low-wage
∗
, the workforce productivity is increasing in wH .
firms). Among high-wage firms with wH > wH
4
Quantitative Implications
In this section we show that our model delivers predictions about the relationships between job
mobility and wages and between internal mobility and firm size which are in line with empirical
evidence. At the same time, we show that those predictions are not easily picked up by standard
job-ladder models.
We calibrate our model to match the following statistics for the U.S. labor market. Set the
time period to a month and let φ = 0.002 reflect an average working life of 40 years. We set
ρ = 0.027 to reflect an average learning period of three years, which we take from Lange (2007).22
∗
Due to the mass point at wH
, the relationship between firm size and workforce productivity is generally
non-monotone.
22
Lange (2007) estimates a model in which employers learn gradually the ability of their employees. His estimate
implies that employers’ initial expectation errors decline by 51% during the first three years of employment and
decline to 36% of their initial value after five years. This suggests that a large part of employer learning occurs
in the first few years of an employment relationship. Although we consider a different learning process, we take
21
18
We set δ = 0.02 to reflect the adjusted layoff rate of Davis et al. (2008) and normalize b = 1.
We set the remaining four parameters, λ (meeting rate), pL and pH (worker productivities), and
α (mass of low-ability workers) to match the following four calibration targets: (1) A monthly
job-to-job transition rate of 2.8%, which corresponds to the average monthly EE rate reported
by Nagypal (2005) based on Current Population Survey data for all workers and which is also
close to her estimates for workers aged 25–34. (2) An average promotion gain of 8%, which
corresponds to the estimate of Pergamit and Veum (1999) based on workers with approximately
10 years in the labor market in the NLSY (see Table 5, specification 2 in their paper).23 (3) An
average quit gain of 3%. (4) An average layoff loss of 4%. These last two calibration targets
correspond to our own estimation results using the NLSY for workers with approximately 10
years in the labor market.24
To calculate the corresponding model statistics, we solve our model for the stationary equilibrium characterized above. We then simulate the labor market transitions of 100,000 workers
during the first ten years of their work life. The parameters are estimated by minimizing the sum
of squared distances between the simulated moments and the data moments. Table 1 shows the
calibrated parameter values and how our model matches the calibration targets stated above.
Table 1: Parameter choices and calibration targets.
Parameter Value
λ
0.118
pL
1.004
pH
1.131
α
0.324
Model statistics
Monthly EE flow
Quit gain
Promotion gain
Layoff loss
Value
2.7%
3.0%
8.0%
4.2%
The calibrated model implies that in equilibrium 29% of firms offer separating contracts,
the Lange (2007) estimate as the best available for our purposes and assume an average learning period of three
years. Using an average learning period of four or five years does not change our main conclusions. In Section
5.2 we briefly discuss the possible implications of gradual learning in our setting.
23
Consistent with the interpretation of our model, Pergamit and Veum (1999) find that in the NLSY most
worker-reported promotions do not involve a change in job title and nearly all promotions involve a wage increase.
In particular, they find that around 56% of those who received a promotion did not change job title and essentially
performed the same duties as before. Only 14% were promoted to a higher-level job in a different section, while
the rest obtained new jobs because of reorganization, a lateral move or because they took their supervisor’s job.
Of all promotions, 89% led to a wage increase. The reported promotion gain of 8% is the average wage change for
all types of promotions. But even promotions that involved performing the same duties as before raised wages
by about 7%.
24
These estimates are obtained by using first differences on the regressions used in Section 4.1 and described
in Appendix C for the period 1987-1994, which is chosen so that the average potential labour market experience
is 10 years. The wage gain estimate after a job-to-job transition is consistent with that of Pergamit and Veum
(1999), Table 5, specification 2.
19
while 71% of firms offer pooling contracts.25 The equilibrium unemployment rate is 16.8%, and
reservation wages are RH = 0.935 < RL = 0.999. Among employed high-ability workers, 47.7%
are in the initial period of a contract, while the rest are promoted to w = pH . Among employed
low-ability workers, 83.7% are in probation (where 89.4% of these workers are found in pooling
firms), 2.2% are promoted to w = pL , while the remaining 14.1% are demoted to w = b. Further,
4.6% of low-ability workers experience wage cuts when making a job-to-job transition.
Our calibrated model also implies that the monthly promotion rate is 1.2%. This statistics
is a bit smaller than the average monthly promotion rate of 2% obtained by Pergamit and Veum
(1999) for workers with around 10 years in the labor market in the NLSY.26 We also obtain a
monthly demotion rate of 0.5%, which implies a promotion-to-demotion ratio of 2.4. Given that
one tends to consider demotions as infrequent events, this number might seem low. However,
Belzil and Bognanno (2008), analyzing a survey of executives in U.S. firms, find that within-firm
promotions are only slightly more frequent than demotions.27
4.1
Worker Mobility and Wage Dynamics
We now analyze the implications for workers’ job mobility and wage dynamics. Is it the case
that workers move to better paying jobs over time, as predicted, for example, by the Burdett
and Mortensen (1998) model? An important finding of Light and McGarry (1998) is that more
separations are negatively related to wages. But as they do not distinguish between separations
into non-employment and job-to-job transitions, those results cannot be directly used to evaluate
our model predictions against other theories of job mobility.
To take different labor market transitions into account, we use a similar sample of the NLSY
as Light and McGarry (1998) and regress the log of real hourly wages on cumulative counts of job∗
Among the firms offering separating contracts, η = 0.05% are at the mass point (pL , wH
), where ξ = 53%
of low-ability workers misreport their type. Note that our wage offer distributions has an increasing an convex
density as in the Burdett and Mortensen (1998) model. The threshold values for ρ described in the previous
sections are ρ1 = 0.123, ρ2 = 0.119 and ρ3 = 0.116. Further, the condition in Lemma 1 holds in this calibration.
26
Note that in the calibration presented above promoted high-ability workers will not experience a second
promotion without first losing their jobs. The latter arises because high-ability workers will not quit their jobs
once they are promoted. This creates a tension with the data in which many workers have more than one
promotion, and these are likely workers of “high ability”. As an alternative calibration, we use the 2% promotion
rate of Pergamit and Veum (1999) as a calibration target which delivers ρ = 0.05. This calibration still produces
a segmented equilibria with very similar properties as the ones discussed in Sections 4.1 and 4.2. In this case we
find that 61% of all employed high-ability workers are promoted, aggravating the tension with the data. Although
not pursued here, one way to address this issue is to introduce a reallocation shock as in Jolivet et al. (2006) or
add firm heterogeneity as suggested in Carrillo-Tudela and Kaas (2011).
27
When defining a promotion (demotion) as an upward (downward) change in reporting levels, the promotionto-demotion ratio is 1.08. When considering only level changes that were accompanied by job title changes,
the promotion/demotion ratio increases to 1.6. If one only considers job title changes, disregarding changes in
reporting level, the promotion/demotion ratio is 5.05. Further, Kramarz et al. (2014), using French administrative
data, find that the promotion/demotion ratio within firms is 3.6 based on occupational changes. See also Lazear
(1992) and Seltzer and Merrett (2000) for evidence on the extent of demotions based on firm case studies.
25
20
to-job transitions and non-employment spells, together with the same number of further controls
that Light and McGarry (1998) used. As Table 2 shows, both coefficients are negative in the OLS
wage regression.28 In light of the literature on earnings losses after displacements (see Jacobson
et al. (1993) for a seminal study), the negative coefficient on the count of non-employment spells
is not surprising. But we also observe a negative correlation between the cumulative count
of job-to-job transitions and current earnings. This goes against the intuition from standard
theories of on-the-job search where workers generally climb up the wage distribution as they
move between employers. Taking intervening non-employment spells into account, as we do in
the wage regressions, one should therefore expect a positive relationship between the number of
past job-to-job transitions and current wages. Indeed, when we run the same wage regression on
simulated data from a Burdett and Mortensen (1998) model, we confirm this insight: more job-tojob transitions correlate positively with wages.29 We further prove in the Appendix (Lemma A.2)
that more job-to-job transitions (counted from the last non-employment spell) in the Burdett
and Mortensen (1998) model indeed lead to higher expected wages.30
The last column in Table 2 shows that the same regression applied to our model can account
for the empirical observations: more job-to-job transitions are negatively correlated with wages,
while again non-employment spells go together with lower earnings. Note that this finding does
not contradict the average wage gain of 3% of a job-to-job transition in our calibration (Table 1).
We argue that the negative link between the count of job-to-job transitions and wages is driven
by worker (unobserved) heterogeneity, both in our model and in the data. To test this, we follow
the procedure described in Light and McGarry (1998) and run IV regressions on our data sample
to account for unobserved worker heterogeneity in the error term. We find that in this case the
coefficient on job-to-job transitions turns positive, while the coefficient on non-employment spells
stays negative (see Appendix C for further details). Hence, standard job ladder models appear
to be fully consistent with the data once worker heterogeneity is accounted for. On the other
hand, those models miss the fact that some workers churn a lot in the labor market and yet
remain largely unsuccessful.31
28
The coefficient estimates shown in Table 2 are obtained using all available years in the NLSY (1979-2010).
Light and McGarry (1998) use the first 8 years of workers’ labor market history. Using the first 8, 10 or 15 years
of workers labor market history does not change our general conclusion. The job-to-job transition coefficients at
8, 10 and 15 years are -0.007, -0.0075 and -0.0081, respectively, all significant at a 1% level. The non-employment
spell coefficients at 8, 10 and 15 years are -0.0137, -0.0140 and -0.0159, respectively, again all significant at a 1%
level. See Appendix C for the data description and a discussion of the regression specifications used.
29
The reported regression results are based on a homogeneous worker version of the model, but it remains true
when we use the two-worker version as in our calibration. It is also not sensitive to the parametrization. We use
the same calibrated parameters as for our model (with α = 0 so that all workers have productivity pH ). In the
simulated data both for our model and for the Burdett and Mortensen (1998) model, workers have very similar
average experience, job duration, number of job-to-job transitions, number of job-to-nonemployment transitions
and non-employment durations; see Appendix C for further details.
30
This theoretical finding is not trivial since workers with few job transitions are predominantly workers who
initially find a good job and hence have less reasons to quit.
31
Light and McGarry (1998) also find considerable variation in mobility patterns. Particularly, the mobility of
some workers does not decline over time, while other workers undergo no or only little job mobility.
21
Table 2: Wage regressions
Data
JTJ
−0.0073
NESP
−0.0185
EXP
0.0431
2
EXP /10 −0.0075
R2
0.331
Models
B-M
CT-K
0.0009 −0.0051
−0.0034 −0.0040
0.0021
0.0055
−0.0005 −0.0010
0.064
0.161
Notes: Data regressions are based on the NLSY, regressions for the Burdett-Mortensen model (B-M) and for our
model (CT-K) are based on simulations of 100,000 workers; for further details about the sample, control variables
and robustness, see Appendix C. JTJ and NESP stand for the cumulative counts of job-to-job transitions and nonemployment spells, EXP is actual labor market experience. All reported coefficients are statistically significant
at the 1% level.
In our model, workers of high-ability climb up the distribution of initial wages with every quit
until they are promoted to their marginal product in which case no further job-to-job transitions
occur unless the worker is displaced. In contrast, low-ability workers misreport their ability level
sometimes, which can lead to demotions and to further job transitions to low-wage employers.32
Hence, low-ability workers undergo much higher job mobility.33
4.2
Internal Mobility and Firm Size
Another feature present in our model that does not come out of a standard job ladder model like
Burdett and Mortensen (1998), is the presence of within firm worker mobility and its relationship with firm size. Our model is able to generate the positive relationship between firm size,
internal mobility, wages and job stability observed in the data. In the calibration larger (pooling)
firms have a 2% higher internal mobility rate (defined as promotions and demotions relative to
employment) than smaller (separating) firms, which is consistent with the evidence obtained by
Idson (1989).34 Alongside this result, we also find that workers in smaller (separating) firms have
32
Consistent with Gibbs et al. (2002) and Belzil and Bognanno (2008), demotions in our model are accompanied
by pay cuts and by subsequent increases in job-transition probabilities.
33
Kahn (2013) also suggests that such composition effects are present in the NLSY data, finding that movers
are on average of lower ability than stayers. In particular, she finds that movers have lower AFQT scores, years
of school, and tenure in the year before they moved, relative to stayers. See Table 2 of her paper for further
details.
34
In the calibration the relative difference in internal mobility between larger and smaller firms depends quite
heavily on the value of ρ. For example, with ρ = 0.05 (as obtained when targeting an average monthly promotion
rate of 2%) implies that larger (pooling) firms have around 17% higher internal mobility than smaller (separating
firms).
22
18% lower tenure than workers in larger (pooling) firms, which is consistent with the empirically
well documented fact that larger employers have lower job separation rates.35
Furthermore, as we establish in Corollary 1, pooling firms have a more productive workforce
than separating firms. We confirm this finding in the calibrated example but note that productivity differences are tiny which is explained by the feature that most workers in the calibration
have high ability and that productivity differences between workers are also not too large. We
do reproduce, however, the usual positive relationships between firm size and wages, consistent
with the empirical evidence (e.g. Brown and Medoff (1989), Idson and Oi (1999)). Although
firms in our model are ex-ante identical, we expect that a similar conclusion obtains if firms
differ in their exogenous productivity level, in which case positive sorting between workers and
firms should obtain in equilibrium.36
Recently, Papageorgiou (2014) presents a theory that is also able to explain the positive
relationship between firm size, internal mobility, wages and job stability. A key difference is
that Papageorgiou (2014) uses occupational mobility within the firm to measure and model the
internal mobility of workers (see also Kramarz et al. (2014)). Further, his theory is based on
workers’ learning about their match quality in a given occupation within the firm and hence is
closely related to that of Jovanovic (1979) and Moscarini (2005). Instead, here we build on search
models in the Burdett and Mortensen (1998) tradition and focus on firms’ learning about the
productivity of a worker. Also Papageorgiou (2014) does not consider long-term wage contracts,
but instead uses spot wages that are determined by Nash bargaining. We see our contributions
as complementary. Using different approaches, both our paper and Papageorgiou (2014) relate
within and between firm mobility in an equilibrium framework in the context of labor market
frictions.
5
Further Discussion
Here we discuss some variations to our assumptions. In Section 5.1 we consider the case in which
firms can observe their applicants’ employment status to analyze whether using this information
makes it easier to separate workers. In this context we analyze two types of contracts: (i) up-orout contracts, where workers that reported their type truthfully get promoted and misreporting
workers are laid off; and (ii) up-or-down contracts as analyzed in the previous sections.37 An
important conclusion from these extensions is that information on employment status strengthens
firms’ monopsony power which makes it easier to separate workers. In Section 5.2 we discuss
alternative assumptions about the firms’ learning process and their implications.
35
Note that in our model the relationship between firm size and job stability is generally ambiguous. This is
because high-wage firms have higher quit rates of demoted low-ability workers.
36
In a previous version of this paper with flat-wage contracts (Carrillo-Tudela and Kaas (2011)), we prove this
assertion.
37
Up-or-out contracts are common practice in some labor markets, such as those for academics, consultants
and lawyers.
23
5.1
Information on Employment Status
Consider the same setup as before, but now firms offer a menu of four contracts ωis = (wis , wi+s , wi−s )
indexed by the worker’s reported ability level i = L, H and employment status s = u, e. The first
component, wis , denotes the initial wage offered to a worker of employment status s that reports
type i. When a firm learns a worker’s type, the worker receives wi+s = pi if he reported his
type truthfully. Otherwise, he receives wi−s . In the case of up-or-out contracts, it is notationally
convenient to assume that firms set wi−s below the worker’s reservation wage, which is equivalent
to a layoff. In the case of up-or-down contracts, wi−s equals the worker’s reservation wage as
analyzed in previous sections. Let Fis denote the corresponding offer distribution of initial wages,
where wsi and wsi denote the infimum and supremum of its support, for i = L, H and s = u, e.
The workers’ value functions are similar to the ones described in equations (19)-(22) and are
described in Appendix D. The main difference is that the offer distributions and their supports
are now indexed by s. The incentive-compatibility constraint is now wjs −wis ≤ ρ[Vi (pi )−Ui ]. The
P
s
s
, wLs for s = u, e.
) + ΩsL (wLs ) by choosing wH
problem of the firm is to maximize s=u,e ΩsH (wH
u
Since firms can perfectly differentiate workers by employment status, they choose (wLu , wH
) and
e
e
(wL , wH ) independently. Hence the problem of hiring workers in the unemployment market can
be treated independently from that of hiring workers in the employment market. Equilibrium
requires that the optimal choices of wis must be consistent with the offer distributions Fis and
the associated function w
bs . Once again we analyze a rank preserving equilibrium such that w
bs
is increasing and FHs (w) = FLs (wˆ s (w)) for each s = u, e and for all w in the support of FHs .
Despite this change, we show that for a sufficiently low learning rate, a segmented equilibrium
emerges with higher turnover of low-ability workers and higher workforce productivity of highwage firms. The key difference between the up-or-out contracts and the up-or-down contracts
is that when a segmented equilibrium arises, up-or-out contracts imply that the unemployment
pool is biased towards low-ability workers.
5.1.1
Up-or-out contracts
Lemma 4: Consider the model where firms offer up-or-out contracts and condition their offers
on employment status. Then, for any initial wages earned by workers of type i = H, L who were
hired from employment (wie ) or from unemployment (wiu ) it holds that wie > wiu .
The above result shows that the supports of the offer distributions FHu and FHe do not overlap. Importantly, this result is independent from whether we have a separating or a segmented
equilibrium. Non-overlapping supports imply that workers hired from unemployment quit as
soon as they get an outside offer during the probation period. Firms then maximize profits by
offering unemployed workers their reservation wage. This leads Fiu to degenerate to a mass point
at wiu = Ri for i = L, H. Further, the incentive-compatibility constraint for low-ability workers
hired from unemployment becomes RH − RL ≤ ρ[VL (pL ) − UL ], which never binds since pH > pL
implies that RL > RH holds for any ρ. This result shows that information on employment status
24
enables firms to exert their full monopsony power when hiring these workers, leading to an outcome similar to that of Diamond (1971), which in turn makes it easier to separate unemployed
workers.
Since workers earning their reservation wage face offer distributions Fie , the infimum of the
support is wei = Ri which is not offered in equilibrium, so that all firms recruit workers hired
from unemployment upon contact. In Appendix D we fully characterize the equilibrium where
firms observe workers’ employment status and use up-or-out contracts. There we show that the
problem faced by firms hiring employed workers turns out to be isomorphic to the one faced
by firms offering promotion/demotion contracts without conditioning on employment status
considered in the previous sections. In particular, the incentive-compatibility constraint for lowe
ability workers hired from employment is now given by wH
− wLe ≤ ρ[pL − b]/(φ + δ). As we
decrease ρ, this constraint starts to bind at high wages. Decreasing ρ further then implies that
firms start offering pooling contracts when the incentive compatible wLe exceeds pL . Therefore
FHe and FLe can be derived in the same way as before and the main insights still apply here.
The difference, however, is that with up-or-out contracts firms do not extract rents from workers
caught misreporting their type, whereas conditioning contracts on employment status allows
firms to strictly increase profits by segmenting its hiring markets.
To illustrate the properties of this version, we provide a quantitative example using the same
calibration targets as in Section 4. When firms can condition their offers on employment status,
reservation wages are lower. This reduces all initial wages in the offer distributions which makes
it easier for firms to separate workers. As a result, the threshold values for parameter ρ where
incentive constraints start and where pooling is the preferred choice for some firms are lower than
in the benchmark model. Indeed, we have that ρ1 = 0.0404 > ρ2 = 0.0395 > ρ3 = 0.0393 . Given
our a value of ρ = 0.027, a segmented equilibrium with pooling at top wages is the outcome.
In this equilibrium low-ability workers have an unemployment rate of uL = 32.8%, while highability workers have an unemployment rate of uH = 28.7%. Reservation wages are RH = 0.911,
RL = 0.993. Different from the benchmark model, however, this model predicts a positive effect
of the count of job-to-job transitions on wages.
In the environment analyzed in this paper, up-or-out contracts could arise, for example, because firms face downward wage rigidities that do not allow them to cut wages. However, without
such imposed constraints, firms will always prefer to use up-or-down contracts. To understand
this, first note that both contracts offer worker the same incentives to report truthfully their
type. Since with up-or-out contracts misreporting workers are laid off, firms make strictly less
profits ex-post relative to up-or-down contracts where firms continue to make profits on demoted
workers. From an ex-ante perspective, firms will also prefer to use up-or-down contracts as they
provide workers with the same incentives as up-or-out contracts. Given these arguments, we now
turn to the case in which firms observe their applicants’ employment status and use up-or-down
contracts.
25
5.1.2
Up-or-down contracts
The analysis of the case of up-or-down contracts is very similar to the one of up-or-out contracts
described in Appendix D.38 With non-overlapping supports of the offer distributions FHu and
FHe , we have that information on employment status once again enables firms to exert their full
monopsony power when hiring unemployed workers, which in turn makes it easier to separate
these workers. Further, the threshold values ρ1 and ρ2 as well as all separating equilibria are
the same as in the previous subsection. The difference arises in the case of segmented equilibria
where demotions (instead of layoffs) occur in equilibrium. A segmented equilibrium with up-ordown contracts therefore has very similar properties to those of the benchmark model considered
in the previous sections.
To illustrate these properties, we calibrate this version of the model using the same targets
as we used for our benchmark model. The model matches the targets reasonably well, exhibiting
a job-to-job transition rate of 2.5%, a quit gain, a layoff loss and a promotion gain of 3.0%,
4.5% and 6.7%, respectively. The cutoff values for the learning rate are ρ1 = 0.0394 > ρ2 =
0.0383 > ρ3 = 0.0380, which implies the calibrated model is characterized by a segmented
equilibrium. In this equilibrium 80.2% of firms offer separating contracts, while 19.8% of firms
offer pooling contracts, reflecting that firms find it easier to separate when they can exert a
higher degree of monopsony power at the hiring stage. The latter is illustrated in the lower
values of unemployed workers’ reservations wages relative to the benchmark model, where RL
and RH are now 0.994 and 0.916, respectively. Further, this calibration exhibits a promotion
rate of 1.4% and a demotion rate of 0.2%, yielding a higher promotion-to-demotion ratio relative
to the benchmark model.
Using this calibration we revisit the implications for wage dynamics and job mobility and the
relationship between firm size and internal mobility. In both cases we find that the predictions
of the benchmark model survive when firms condition their contracts on workers’ employment
status. In particular, we perform the same exercise as described in Table 2 and obtain that
the coefficient for the cumulative count of job-to-job transitions remains negative, although it
is now one order of magnitude lower relative to the benchmark case (-0.0002 vs -0.005). The
coefficient for the cumulative count of non-employment spells also remains negative and of similar
magnitude as before (-0.007 vs -0.004). Regarding internal mobility and firm size, we find that
the internal mobility rate is 14% higher in larger (pooling) firms relative to smaller (separating)
firms. We also find that jobs in smaller (separating) firms have 2.6% lower tenure than those in
larger (pooling) firms, as well as a positive relationship between wages and firm size.
38
Given the similarity between the two analyses, we do not present the case of up-or-down contracts. The
only substantial difference is that the profits of pooling firms include an additional term which reflects the profits
earned on demoted workers, which is similar to the proof of Proposition 2.
26
5.2
Firms’ Learning Process
In the framework of our model, firms learn worker ability with certainty at Poisson rate ρ. This is
clearly a strong abstraction which masks many important features of real-world employer learning. In a more general model, the firm would draw signals which are imperfectly correlated with
the worker’s ability, so that the firm has to update its beliefs about worker ability with every new
signal. While such learning processes are often applied in simpler environments, they tremendously complicate the analysis in our model, given that we allow wage contracts to be contingent
on all verifiable information. A wage contract in such a general model should specify sequences
of flow wages (w(sn ))n≥0 which are contingent on the signal histories sn = (s0 , s1 , . . . , sn ) where
signals arrive at an exogenous Poisson rate. Even with a finite (e.g. two state) signal space, the
firm’s contracting problem and the corresponding equilibrium analysis would complicate greatly.
Alternatively, contracts could be restricted to a one time promotion/demotion only. In such a
world, making signals reveal partial information restrains the firm’s ability to promote or demote the worker; thus it should be harder for the firm to satisfy incentive compatibility. This,
we conjecture, would lead to more pooling in equilibrium.
One can also think about further elaborating the learning process by letting the firm decide
ρ. A natural way to endogenize ρ is by letting firms choose costly monitoring intensity m,
such that an increasing function ρˆ(m) determines the learning rate for any given m ≥ 0. An
obvious question in such a setting is which firms in the wage-offer distribution use more intensive
monitoring. Given that incentive constraints are tighter in the upper part of the wage-offer
distribution, we conjecture that high-wage firms spend more on monitoring and therefore are
able to promote (or demote) workers faster; this mechanism would strengthen our previous result
that larger firms have higher internal mobility rates. By varying parameters of the monitoring
cost function, the optimal choices of ρ will change and we could perform the same exercises as
done so far to understand firms’ ability to separate workers when information frictions change
relative to search frictions.
6
Conclusions
In this paper we consider a model of the labor market in which search frictions coexist with
information frictions. The latter arise as firms do not observe worker ability upon hiring but
gradually learn it over time. Given this adverse selection problem, we show that when the
learning rate is sufficiently low, an equilibrium emerges in which low-wage firms attempt to
hire both low- and high-ability workers by offering incentive-compatible separating contracts.
These contracts offer initially a low wage and then promote the worker by increasing his wage
to marginal productivity. High-wage firms, however, offer contracts that pay the same initial
wage to all workers, but after learning their employees’ types they promote high-ability workers
and demote low-ability workers. This implies that low-ability workers can experience a wage
cut or a wage rise when undertaking a job-to-job transition, while high-ability workers can only
27
experience wage rises when changing jobs without an intervening spell of unemployment.
In such a segmented equilibrium, low-ability workers have a higher degree of job turnover and
lower average earnings than high-ability workers. To gain further insights on this relationship,
we calibrate our model and show that it generates indeed a negative overall relationship between
the number of job-to-job transitions and wages, which is consistent with the evidence that we
obtain in NLSY data, extending the empirical findings of Light and McGarry (1998). Such a
negative relationship is not easily picked up by standard models of job-to-job mobility, such as
Burdett and Mortensen (1998), where workers generally climb up the wage ladder as they move
between employers.
It should be an interesting extension to include different occupations and assignment problems
within the firm. For example, suppose that firms aim to assign workers into one of two different
occupations, such that only high-ability workers can efficiently perform the “high occupation”,
yielding output pH , whereas low-ability workers should be assigned to the “low occupation”,
producing output pL <pH . Any mismatch between workers’ abilities and occupations yields
(weakly) lower output levels. If a worker self-selects to the right occupation/contract, the firm
promotes the worker after learning his type, but if he is caught misreporting, the firm re-assigns
the worker to the correct occupation and pays the demotion wage. In such a setting, this model
could speak to occupational mobility within and across firms.
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Appendix A: Worker strategies
Let Ui denote the value of unemployment of a worker with ability i = L, H. Note that once this worker
encounters a potential employer, the firm does not observe his ability, so that the worker can claim to be
of different ability. For any contract ω = (w, w+ , w− ), let Vij (ω) denote the maximum expected value of
employment for a worker with ability i employed in probation at initial wage w after reporting type j.
We can think of these workers as randomly meeting firms who draw contract offers (ωH , ωL ) from joint
distribution Ψ. The worker then decides which contract to choose (if any) to maximize expected lifetime
income. Using this insight and standard dynamic programming arguments, the Bellman equation that
describes Ui is given by
Z
φUi = b + λ max[ViL (ωL ) − Ui , ViH (ωH ) − Ui , 0]dΨ(ωH , ωL ) .
(19)
The value of employment for a worker of ability i employed in contract ωi = (wi , wi+ , wi− ) at the initial
wage is given by
Z
0
0
φVii (ωi ) = wi + λ max[ViL (ωL0 ) − Vii (ωi ), ViH (ωH
) − Vii (ωi ), 0]dΨ(ωH
, ωL0 )
(20)
+δ(Ui − Vii (ωi )) + ρ(Vi (wi+ ) − Vii (ωi )) ,
where the continuation value after promotion is given by
Z
+
+
0
0
φVi (wi ) = wi + λ max[ViL (ωL0 ) − Vi (wi+ ), ViH (ωH
) − Vi (wi+ ), 0]dΨ(ωH
, ωL0 ) + δ(Ui − Vi (wi+ )) . (21)
Now consider a worker of type i that misreported his type and is currently earning the initial wage wj
in contract ωj = (wj , wj+ , wj− ). This worker’s value function is described by
Z
0
0
φVij (ωj ) = wj + λ max[ViL (ωL0 ) − Vij (ωj ), ViH (ωH
) − Vij (ωj ), 0]dΨ(ωH
, ωL0 )
(22)
+δ(Ui − Vij (ωj )) + ρ(Vi (wj− ) − Vij (ωj )) .
Finally, the continuation value after a demotion is given by
Z
0
0
φVi (wj− ) = wj− + λ max[ViL (ωL0 ) − Vi (wj− ), ViH (ωH
) − Vi (wj− ), 0]dΨ(ωH
, ωL0 ) + δ(Ui − Vi (wj− )) . (23)
From (20) and (22), it is easy to see that worker i’s incentive constraint Vii (ωi ) ≥ Vij (ωj ) can be
expressed as wj − wi ≤ ρ[Vi (wi+ ) − Vi (wj− )], which is (1) in the main text.
When we consider simple contracts ωi = (w, pi , b), we simplify notation by expressing workers’ value
functions as Vii (w) etc. rather than Vii (ωi ). In those situations it is straightforward to verify that any
worker’s optimal search strategy is described by a reservation wage. Let Rijk (x) denote the reservation
(initial) wage of a worker in a probation contract who (i) currently receives flow payoff x, (ii) is of
type i = L, H, (iii) has reported type j = L, H, and (iv) when meeting a firm decides to report type
k = L, H. Thus, Rijk (x) is defined by Vij (x) = Vik (R). Similarly, Rik (x) is the reservation (initial)
wage of a promoted/demoted worker with flow income x, which is defined by Vi (x) = Vik (R). The
above value functions imply that an unemployed worker of type i accepts a wage offer w0 if and only if
w0 ≥ Rik (b) for i, k = L, H.
We write Ri ≡ Rii (b) for the reservation (initial) wage of an unemployed worker of type i who
reports his true type. Those reservation wages are smaller than b since truth-telling workers can expect
a promotion to wi = pi > b at rate ρ.
32
Consider an employed worker of type i that reported his true type and is earning initial wage wi .
Given contact with a firm and revealing his true type once again (i.e. k = i), (20) implies that this
worker accepts employment if and only if the firm offers a wage wi0 > Riii (wi ) = wi . If the worker decides
to misreport his type (i.e. k 6= i), however, (20) and (22) imply that the worker accepts employment
if and only if the firm offers a wage wk0 > Riik (wi ) = wi + ρ[Vi (pi ) − Ui ]. In this case, the worker must
be compensated by the expected loss of misreporting his type. Next consider the same worker after his
employer has learned his true type and is earning wage pi . Given contact with a firm and revealing his
true type (i.e. k = i), (20) and (21) imply that this worker accepts employment if and only if the firm
offers an initial wage wi0 > Rii (pi ) = pi . If this worker decided to misreport his type, (21) and (22) imply
that the worker accepts employment if and only if the firm offers a wage wk0 > Rik (pi ) = pi +ρ[Vi (pi )−Ui ].
Now suppose that an employed worker of type i misreported type j 6= i and is earning the initial
wage wj . Given contact with a firm and reporting his true type (k = i), (20) and (22) imply that the
worker accepts employment if and only if the firm offers a wage wi0 > Riji (wj ) = wj − ρ[Vi (pi ) − Ui ]. In
this case, the worker voluntarily accepts a wage cut since the truth-telling worker expects a promotion
gain relative to the demotion loss. On the other hand, if the worker misreports his type once again
(k = j), the worker accepts employment if and only if the firm offers a wage wj0 > Rijj (wj ) = wj .
Finally consider the same worker after his employer has learned his true type, earning demotion wage
b. This worker then behaves like an unemployed worker and accepts any contract that provides utility
greater than the continuation value from unemployment.
33
Appendix B: Proofs
Proof of Lemma 1
Consider a candidate equilibrium in simple contracts.PThat is, for anyPcontract pair (ωi )i=H,L =
(wi , pi , b)i=H,L in the support of Ψ, it holds that Ω∗ ≡ i=H,L Ωi (ωi ) ≥ i=H,L Ωi (ωi0 ) for all pairs
of simple contracts (ωi0 )i=H,L = (wi0 , pi , b)i=H,L . To prove the Lemma, we need to show that no other
feasible contract pair of arbitrary form (ˆ
ωi )i=H,L = (w
ˆi , w
ˆi+ , w
ˆi− )i=H,L can lead to higher profit value
than Ω∗ . Feasibility requires that wi , wi+ , wi− ≤ pi and wi+ , wi− ≥ b (otherwise the firm or the worker
would quit the contract).
Consider first the situation where the deviating contract pair (ˆ
ωi )i=H,L is incentive compatible,
i.e. for i 6= j,
w
ˆj − w
ˆi ≤ ρ[Vi (w
ˆi+ ) − Vi (w
ˆj− )] .
(24)
Note that Vii (ˆ
ωi ) ∈ [Ui , Vi (pi )]: Vii (ˆ
ωi ) cannot be smaller than Ui (otherwise the contract would not
attract any workers), and it cannot exceed Vi (pi ) because of the feasibility restrictions w
ˆi , w
ˆi+ ≤ pi .
0
0
0
Hence, for both i = H, L, there exist simple contracts ωi = (wi , pi , b) such that Vii (ωi ) = Vii (ˆ
ωi ). The
starting wage wi0 is then pinned down by
wi0 + ρVi (pi ) = w
ˆi + ρVi (w
ˆi+ ) .
(25)
Now it follows that the pair of simple contracts (ωi0 )i=H,L is also incentive-compatible: for any j 6= i
wj0
= w
ˆj + ρ[Vj (w
ˆj+ ) − Vj (pj )]
≤ w
ˆi + ρ[Vi (w
ˆi+ ) − Vi (w
ˆj− )]
= wi0 + ρ[Vi (pi ) − Vi (w
ˆj− )]
≤ wi0 + ρ[Vi (pi ) − Vi (b)] .
Here the two equalities make use of (25), the first inequality makes use of (24) and w
ˆj+ ≤ pj (which implies
Vj (w
ˆj+ ) ≤ V
ˆj− ≥ b (which implies Vi (w
ˆj− ) ≥ Vi (b)).
j (pj )), and the second inequality makes use of w
P
Because of i=H,L Ωi (ωi0 ) ≤ Ω∗ , contract pair (ˆ
ωi )i=H,L does not lead to higher profit than Ω∗ if we can
0
prove that Ωi (ˆ
ωi ) ≤ Ωi (ωi ) for i = H, L. To show this assertion, note that
Ωi (ωi0 ) = `0i [pi − wi0 ]
and
h
i
p −w
ˆi+
,
Ωi (ˆ
ωi ) = `ˆi pi − w
ˆi + ρ i
φ + δ + λˆ
qi
where `0i and `ˆi are the masses of workers of type i who are employed in the starting phases of the two
ωi ), both contracts attract the same number of type i workers who
contracts. Because of Vii (ωi0 ) = Vii (ˆ
have the same quit rates in the starting phase of the contracts; hence `0i = `ˆi . The terms in [.] are the flow
profits for each of these workers; these contain the flow profit pi − wi0 (pi − w
ˆi ) and a continuation profit
value which is realized at flow rate ρ when the worker is promoted (which is zero for the simple contract
ωi0 ). qˆi is the probability that worker i who is promoted to wage w
ˆi+ quits this contracts when meeting
another firm. Because of these expressions and (25), the requirement Ωi (ˆ
ωi ) ≤ Ωi (ωi0 ) is equivalent to
showing that
pi − w
ˆi+
Vi (pi ) − Vi (w
ˆi+ ) ≥
.
(26)
φ + δ + λˆ
qi
From workers’ Bellman equations follows
Vi (pi ) =
pi + δUi + λE{max[Vi (pi ), V˜i ]}
φ+δ+λ
and
34
Vi (w
ˆi+ ) =
w
ˆi+ + δUi + λE{max[Vi (w
ˆi+ ), V˜i ]}
,
φ+δ+λ
where V˜i is worker i’s continuation utility from a random outside offer. It follows
Vi (pi ) − Vi (w
ˆi+ ) =
≥
pi − w
ˆi+ + λE{max[Vi (pi ), V˜i ] − max[Vi (w
ˆi+ ), V˜i ]}
φ+δ+λ
+
pi − w
ˆi + λ[Vi (pi ) − Vi (w
ˆi+ )](1 − qˆi )
.
φ+δ+λ
Rearranging proves (26).
Second, suppose that the deviating contract pair (ˆ
ωi )i=H,L is not incentive compatible so that all
workers pool in contract ω
ˆ H . The alternative scenario where both workers pool in contract ω
ˆ L is then
+
−
captured as well: if both workers would pool in contract ω
ˆ L = (w
ˆL , w
ˆL , w
ˆL ), we can define contract
+
−
+
−
−
+
ω
˜ H = (w
˜H , w
˜H
,w
˜H
) by w
˜H = w
ˆL , w
˜H
=w
ˆL
,w
˜H
=w
ˆL
, and pick an arbitrary unattractive contract
ω
˜ L , so that all workers pool in contract ω
˜ H . We can therefore consider the case where all workers pool
in some contract ω
ˆ H and we need to prove that ΩH (ˆ
ωH ) ≤ Ω∗ . We can write
− i
+ i
h
h
pH − w
ˆH
pL − w
ˆH
+`ˆL pL − w
ˆH + ρ
,
ΩH (ˆ
ωH ) = `ˆH pH − w
ˆH + ρ
φ + δ + λˆ
qH
φ + δ + λˆ
qL
{z
}
{z
}
|
|
≡π
ˆH
≡π
ˆL
where `ˆi is steady-state employment of type i workers in the starting phase of this contract and qˆi ,
i = H, L, are the probabilities that promoted/demoted workers of type i quit contract ω
ˆ H when outside
offers arrive. As in the first part of the proof, because of VHH (ˆ
ωH ) ∈ [UH , VH (pH )], there exists a simple
0 = (w 0 , p , b) such that V
0 )=V
contract ωH
(ω
(ˆ
ω
).
This
implies that
HH
HH
H
H H
H
+
0
wH
+ ρVH (pH ) = w
ˆH + ρVH (w
ˆH
).
(27)
0 attracts the same mass of H-workers as ω
Because contract ωH
ˆ H , and quit rates in the starting phase
0 yields higher profit per worker of
0
ˆ
are also the same, it follows that `H = `H . The simple contract ωH
p −w
ˆ+
0 ≡ p − w0 ≥ π
0 ≥ ρ H
H
type H if πH
ˆH which is equivalent to w
ˆ H − wH
H
H
φ+δ+λˆ
qH , which because of (27) is
equivalent to
+
pH − w
ˆH
+
)≥
VH (pH ) − VH (w
ˆH
.
(28)
φ + δ + λˆ
qH
+
w
ˆ +δUH +λˆ
qH VˆH
+δUH
+
) = H φ+δ+λˆ
Note that VH (pH ) = pHφ+δ
and VH (w
ˆH
where VˆH is the expected continuation
qH
+
. Substitution into (28) and rearranging yields the equivalent inequalutility for a H-worker quitting wH
ity
p + δUH
VˆH ≤ H
= VH (pH ) ,
φ+δ
which is fulfilled since no firm can offer a greater continuation utility than VH (pH ). This proves that
the simple contract yields (weakly) greater profit on H workers:
0
`0H πH
≥ `ˆH π
ˆH .
(29)
To prove that ΩH (ˆ
ωH ) ≤ Ω∗ , we distinguish between two cases: π
ˆL ≥ 0 and π
ˆL < 0. In the first
0 and such that contract
one, we can construct a simple contract ωL0 that is incentive-compatible to ωH
0 , ω 0 ) dominates pooling contract ω
pair (ωH
ˆ H . In the second case other arguments are required.
L
−
0 = w
Suppose first that π
ˆL ≥ 0. By defining wL
ˆH − ρ[VL (pL ) − VL (w
ˆH
)], the simple contract
0
0
ωL = (wL , pL , b) yields the same utility to L-workers as the pooling contract: VLL (ωL0 ) = VLH (ˆ
ωH ).
0 ≤ p . This follows because of
Moreover, the simple contract is feasible, i.e. wL
L
−
VL (pL ) − VL (w
ˆH
)≥
35
−
pL − w
ˆH
,
φ + δ + λˆ
qL
which follows from a similar argument as (26), and because of π
ˆL ≥ 0:
−
0
wL
=w
ˆH − ρ[VL (pL ) − VL (w
ˆH
)] ≤ pL − π
ˆL + ρ
−
−
p −w
ˆH
pL − w
ˆH
−ρ L
≤ pL .
φ + δ + λˆ
qL
φ + δ + λˆ
qL
0 ≥π
0 , ω 0 ) is incentive-compatible
This also proves that πL0 = pL − wL
ˆL . The pair of simple contracts (ωH
L
0 ). Here the inequality follows because contract ω 0 promises a
since VLL (ωL0 ) = VLH (ˆ
ωH ) ≥ VLH (ωH
H
0 and
lower starting wage and a lower continuation wage to L-workers than contract ω
ˆ H (i.e. w
ˆ H ≥ wH
−
0
0
w
ˆH ≥ b). Therefore, and because of VLL (ωL ) = VLH (ˆ
ωH ), simple contract ωL when offered jointly with
0
ωH attracts the same number of L-workers as pooling contract ω
ˆ H . Hence `0L = `ˆL which implies
`0L πL0 ≥ `ˆL π
ˆL .
(30)
0 , ω 0 ) yields profit not greater than Ω∗ , it follows from (29) and
Because the pair of simple contracts (ωH
L
∗
(30) that ΩH (ˆ
ωH ) ≤ Ω .
Suppose second that π
ˆL < 0. Here we again need to distinguish between two situations. The first
is the case where only separating contracts are offered in the candidate equilibrium. In this situation,
0 is smaller than Ω∗ and it provides an upper bound for the deviating pooling contract ω
`0H πH
ˆ H , as
we show in the next paragraph. In the other situation where some pooling occurs in the candidate
equilibrium, further arguments are required.
Consider first the case in which all firms offer separating contracts in the candidate equilibrium
0 provides an upper bound for Ω (ˆ
(cf. Proposition 1). Because of (29) and π
ˆL < 0, `0H πH
H ωH ). Hence, the
0 ≤ Ω∗ . Write
deviating contract (ˆ
ωH , ω
ˆ L ) does not lead to higher profit than Ω∗ if we can show that `0H πH
wH for the highest equilibrium starting wage offered to H-workers, and let `H denote the employment
of H-workers in the starting phase of this contract. π H = pH − wH is the profit flow for each of these
0 ≥ w , it follows that π 0 ≤ π . Moreover, since contract (w 0 , p , b) does not attract
workers. If wH
H
H
H
H H
or retain any more H-workers than contract (wH , pH , b) (because the equilibrium distribution FH has
no mass point at wH as shown in Proposition 1), it follows that `0H = `H . Hence,
0
`0H πH
≤ `H π H < `H π H + `L π L = Ω∗ .
0 < w , w 0 is in the support of the equilibrium wage-offer distribution (cf. Proposition
Conversely, if wH
H
H
0 , p , b) exists such that `0 π 0 < `0 π 0 + `0 π 0 =
1). Hence, a feasible incentive-compatible contract (wL
L
H H
H H
L L
∗
Ω .
Consider now the case in which π
ˆL < 0 and some firms offer pooling contracts in the candidate
equilibrium so that the arguments of the previous paragraphs do not apply. In this case there may not
0 and yields the same
exist a feasible simple contract ωL0 which is incentive compatible to contract ωH
−
0 ≤ w
utility to L-workers as pooling contract ω
ˆ H . Because of wH
ˆH and b ≤ w
ˆH , the simple contract
0
0
ωH = (wH , pH , b), when offered as a pooling contract, is less attractive to L workers than pooling
contract ω
ˆ H and it also retains fewer of those workers; hence `0L ≤ `ˆL . We further claim that the profit
from any L worker in the simple contract is no smaller than the one with contract ω
ˆ H , i.e.
−
0
πL0 = pL − wH
+
pL − w
ˆH
pL − b
≥π
ˆ L = pL − w
ˆH + ρ
.
φ+δ+λ
φ + δ + λˆ
qL
0 ≤w
Because of wH
ˆH , this follows if
−
pL − w
ˆH
pL − b
≥
.
φ+δ+λ
φ + δ + λˆ
qL
36
(31)
Consider any arbitrary demotion wage w− and define function
H(w− ) ≡
pL − w −
,
φ + δ + λ[1 − FL (w(w
ˇ − ))]
where w(w
ˇ − ) is the initial wage of a simple contract that yields the same continuation payoff to worker
L as the flat demotion wage w− , so that [1−FL (w(w
ˇ − ))] is the probability that L-workers quit demotion
−
−
wage w . Therefore, H(w
ˆH ) equals the right-hand side in condition (31). The wage w(w
ˇ − ) satisfies
VLL (w(w
ˇ − ), pL , b) = VL (w− ) (and hence w(b)
ˇ
= RL ). With this notation, we can also define Γ(w) ≡
−
−1
H(w
ˇ (w)) for initial wages w ≥ RL . Condition (31) for any feasible value of w
ˆH
is then equivalent to
−1
Γ(w) ≤ Γ(RL ) for all w ∈ [RL , pL ]. The relation VLL (w, pL , b) = VL (w
ˇ (w)) can also be expressed as
w
ˇ −1 (w) = w + ρ[VL (pL ) − VLL (w, pL , b)] ,
so that we have
0
φ + δ + λ(1 − FL (w))
0
(w, pL , b) =
,
w
ˇ −1 (w) = 1 − ρ d VLL
dw
φ + δ + ρ + λ(1 − FL (w))
which makes use of the derivative of (4) which applies to all wages w ≤ pL . Therefore, integration
implies
Z w
φ + δ + λ(1 − FL (w0 ))
0
−1
w
ˇ (w) = b +
0 dw ,
φ
+
δ
+
ρ
+
λ(1
−
F
(w
))
L
RL
so that
Γ(w) =
pL − b −
φ+δ+λ(1−FL (w0 ))
0
RL φ+δ+ρ+λ(1−FL (w0 )) dw
Rw
φ + δ + λ(1 − FL (w))
.
With the condition of Lemma 1, the requirement Γ(w) ≤ Γ(RL ) is fulfilled so that π
ˆL ≤ πL0 . This,
0
ˆL . Therefore, the simple pooling contract ωH
ˆL < 0 proves that `0L πL0 ≥ `ˆL π
together with `0L ≤ `ˆL and π
0
0
0
0
0
ˆ
ˆ
yields total profit ΩH (ωH ) = `H πH + `L πL which is at least as large as ΩH (ˆ
ωH ) = `H π
ˆH + `L π
ˆL . This
0
∗
proves that ΩH (ˆ
ωH ) ≤ ΩH (ωH ) ≤ Ω .
2
Proof of Lemma 2
Note that a worker does not misreport his type whenever the incentive-compatibility constraint
Vii (wi ) ≥ Vij (wj ) holds for any offered pair (wi , wj ). Using (20) and (22), it follows that this is
equivalent to
wj − wi ≤ ρ[Vi (pi ) − Ui ] ,
which is identical to the incentive constraint (1). We can simplify this equation by making use of the
reservation wage equation
Ri = b − ρ[Vi (pi ) − Ui ] ,
(32)
where Ri = Rii (b) < b is the reservation initial wage of an unemployed worker of type i who reports
truthfully. Using this equation, we can rewrite the incentive constraints as (2).
2
Proof of Proposition 1
To express the dependance on ρ, we write Ri (ρ), i = H, L, for the reservation wages, and wi (ρ) for
the highest wages in the support of the offer distributions. The separating equilibrium characterized in
Section 3.2 is feasible provided that wL (ρ) ≤ pL which is equivalent to
wH (ρ) ≤ pL + b − RL (ρ) .
37
(33)
This inequality is strictly fulfilled as long as incentive constraints do not bind (that is, if ρ ≥ ρ1 ), because
of wL < pL . On the other hand, when ρ tends to zero, RL (ρ) → b, while
h
i
(φ + δ)2 (p − (1 + α)b)
1
wH (ρ) → wH (0) = 1 +
p
−
.
2
α
(λ + φ + δ)
Because (18) is equivalent to wH (0) > pL , inequality (33) fails if ρ < ρ1 is sufficiently small. Hence,
under condition (18), there exists ρ2 ∈ (0, ρ1 ) such that the separating equilibrium is feasible for any
ρ ≥ ρ2 . On the other hand, if (18) fails, either (33) holds for all ρ ∈ [0, ρ1 ], in which case the separating
equilibrium is feasible for all ρ ≥ ρ2 = 0, or condition (33) fails for some values ρ ∈ [0, ρ1 ] in which case
ρ2 > 0 is defined as the supremum of those values of ρ where (33) holds with equality.
Conditional on ρ ≥ ρ2 , we first solve for equilibrium reservation wages when incentive constraints
bind. Define
λ(1 − Fi (w))
hi (w) ≡
, i = L, H ,
φ + δ + ρ + λ(1 − Fi (w))
and split the integral expressions in the reservation wage equations (13) as follows:
Z w˜H
hH (w)dw = w
˜H − RH + 2C(Y 1/2 − 1)(pH − RH ) ,
Z
RH
wH
hH (w)dw = wH − w
˜H +
w
˜H
w
˜L
Z
Z
i
2C h
C(p − R) − (p − R)1/2 (p + α(b − RL ) − (1 + α)w
˜H )1/2 ,
1+α
hL (w)dw = w
˜L − RL + 2C(Y 1/2 − 1)(pL − RL ) ,
RL
wL
hL (w)dw = wL − w
˜L +
w
˜L
where we define Y ≡
i
2C h
C(p − R) − (p − R)1/2 (p + α(b − RL ) − (1 + α)w
˜H )1/2 ,
1+α
pH −b−pL +RL
pH −RH −pL +RL .
Z
Adding up the integral expressions gives
wH
hH (w)dw =
RH
i
1 h
(p − R)(1 + C 2 ) + α(b − RH )
1+α
α
+2C
[pH − b − pL + RL ]1/2 [pH − RH − pL + RL ]1/2 − 2C(pH − RH )
1+α
and
Z
wL
hL (w)dw =
RL
i
1 h
(p − R)(1 + C 2 ) + RH − b
1+α
1
−2C
[pH − b − pL + RL ]1/2 [pH − RH − pL + RL ]1/2 − 2C(pL − RL ) .
1+α
Substitution of these terms into the reservation wage equations (13) yields two nonlinear equations that
determine RL and RH simultaneously. Adding the equation for RH to the one for RL multiplied by α,
we see that the nonlinear term disappears so that we can solve for R = RH + αRL :
R=
pρC(C − 2) + b(1 + α)(ρ + φ + δ)
.
φ + δ + ρ(1 − C)2
We can now substitute RH = R − αRL into the reservation wage equation for RL , which is quadratic
in RL . The relevant root is obtained as follows:
p
4C 2 (F (1 + α) + G) − 2DE + [4C 2 (F (1 + α) + G) − 2DE]2 − 4(4C 2 (1 + α) − E 2 )(4C 2 F G − D2 )
RL =
,
2E 2 − 8C 2 (1 + α)
38
with
D ≡ b[(1 + α)
φ+δ
+ α] + p(1 + C 2 ) − pL (1 + α)(1 + 2C) − RC 2 ,
ρ
E ≡ (1 + α)[2C −
φ+δ
] − α , F ≡ pH − b − pL , G ≡ pH − R − pL .
ρ
These reservation wages, together with w
˜i from (11), wH from (17), wL = wH − b + RL , and the
wage offer distributions from (8) and (9), characterizes the candidate equilibrium with binding incentive
constraints. To prove that the candidate equilibrium indeed is an equilibrium, we still need to show that
no separating firm finds it optimal to deviate to a simple pooling contract. We formulate this assertion
as Lemma A.1 below. Because of this Lemma and Lemma 1, the candidate equilibrium is a market
equilibrium.
2
Lemma A.1: For any ρ ≥ ρ2 , firms do not find profitable deviations to a simple pooling contract.
Proof: Consider a firm offering a simple pooling contract ω
˜ = (wH , pH , b) such that wH ≤ wH , to
retain high-ability workers. Note that offering a pooling contract (wH , pH , b) in which wH > wH is not
profitable since this contract has the same hiring and retention rate of workers as the pooling contract
(wH , pH , b), but leads to lower profit per worker.
Instead of offering the pooling contract ω
˜ = (wH , pH , b), the firm can also offer a menu of separating
contracts (ωH , ωL ) with ωH = ω
˜ and ωL = (w(w
ˆ H ), pL , b), w(w
ˆ H ) = wH − b + RL ≤ pL . The pooling
˜ (Ω) satisfying
(separating) contracts, conditional on hiring a worker, yield expected profit values Ω
i
h
˜ = `˜H [pH − wH ] + `˜L pL − wH + ρ pL − b
Ω
,
φ+δ+λ
Ω = `H [pH − wH ] + `L [pL − w(w
ˆ H )] ,
where `˜i and `i are the numbers of workers of ability i in the starting phase of the two contracts. Note
that both contracts have the same hiring and quit rates for both worker types in the pre-promotion
stage since FL (w(w
ˆ H )) = FH (wH ) and low-ability workers are indifferent between reporting type L or
type H at the offered contract wages. Therefore, `i = `˜i for i = H, L, and the pooling contract strictly
dominates the separating contract if and only if
pL − w(w
ˆ H ) < pL − wH + ρ
pL − b
,
φ+δ+λ
which is equivalent to (see (5) and (6))
wH − w(w
ˆ H) = ρ
This in turn is the same as
φUL >
pL − φUL
pL − b
<ρ
.
φ+δ
φ+δ+λ
λpL + (φ + δ)b
.
φ+δ+λ
(34)
On the other hand, we have that
Z
wL
(φ + λ)UL = b + λ
VLL (w)dFL (w) < b + λ
RL
pL + δUL
,
φ+δ
since no contract offered to low-ability workers yields utility value greater than (pL + δUL )/(φ + δ). But
this inequality is equivalent to
λpL + (φ + δ)b
φUL <
,
(35)
φ+δ+λ
39
which contradicts (34) and thus proves that the separating contract dominates the pooling contract
when ρ ≥ ρ2 . This completes the proof of Lemma A.1.
2
Proof of Lemma 3
We first show that firms make negative expected profit on any low-ability worker hired in a pooling
∗ =w
contract with initial wage wH ≥ wH
ˆ −1 (pL ), i.e.
pL − wH + ρ
pL − b
<0,
φ+δ+λ
for all wH ≥ pL + b − RL . This is true if and only if
ρ
pL − b
pL − φUL
= b − RL > ρ
.
φ+δ
φ+δ+λ
In the proof of Proposition 1 we show that this inequality is fulfilled (see equation (35)).
∗ =
To prove the first claim, suppose there is no mass point. Then ρ < ρ2 implies that wH > wH
−1
∗
w
ˆ (pL ) so that some firms offer pooling contracts at wH + ε. In the limit ε → 0, the inflow (quit)
rates of high-ability workers at these firms are identical to the inflow (quit) rates of high-ability workers
∗ . However, for ε → 0, the inflow rate of low-ability
at firms with the highest separating contract at wH
∗
∗
workers is strictly larger at wH + ε than at wH since the former contract attracts the mass of promoted
low-ability workers (earning pL ) whereas the latter contract does not. Hence, profit would jump down
∗ .
discontinuously since firms make negative profits on low-ability workers in a pooling contract wH ≥ wH
This contradicts profit maximization.
To prove the second claim, suppose that all low-ability workers who are offered separating contracts
∗ , p ) report truthfully. Then firms offering this contract earn zero profits on low-ability workers
(wH
L
∗ − ε and
and positive profits on high-ability workers. A firm offering a separating contract at wH
∗ − ε), however, also earns (nearly) zero profit on low-ability workers and it has the same
wL = w(w
ˆ H
inflow rate of high-ability workers in the limit ε → 0; however, the quit rate of high-ability workers
∗ − ε to w ∗ because workers earning w ∗ − ε (w ∗ ) quit (do not quit)
jumps down discontinuously from wH
H
H
H
∗
∗ , profits jump up discontinuously
to another firm offering wH . Since there is a mass of firms offering wH
∗ − ε to w ∗ , which again contradicts profit maximization.
from wH
H
This completes the proof of Lemma 3.
2
Proof of Proposition 2
The proof proceeds in two steps. We first characterize the vector of endogenous variables E ≡
(ϕ, ξ, η, RL , RH ) by a set of equilibrium conditions. Second, we prove that the candidate equilibrium
exists using Brouwer’s fixed-point theorem.
Steady State Measures
We write Gi (w) for the earnings distribution of initial wages and G∗i (w) for the earnings distribution
of wages after promotions/demotions. Since the latter has mass points at pi and at b and zero density
elsewhere, we write gi∗ (pi ), i = H, L, and gL∗ (b) for the measures of employed workers after promo∗ , p ), we write g (p ),
tion/demotion. Since the distribution of initial wages has a mass point at (wH
L
L L
∗
∗
∗ (high and low ability)
gL (wH ) and gH (wH ) for the measures of workers earning pL (low ability) or wH
before promotion/demotion decisions. We calculate these earnings distribution measures as functions
of equilibrium variables E as follows.
1. Low-ability workers
∗ )−G
∗
∗
Write g1 = GL− (pL ), g2 = GL (pL ) − GL− (pL ) = gL (pL ), g3 = GL (wH
L− (wH ) = gL (wH ),
∗
∗
∗
g4 = GL (wH ) − GL (wH ), g5 = g (b), g6 = g (pL ). Thus, fraction G0 ≡ g1 + g2 + g3 + g4 of employed
low-ability workers receive initial wages and fractions g5 (g6 ) have been demoted (promoted). Hence,
40
∗ ), so that
G0 + g5 + g6 = 1. Note that no low-ability worker earns a wage in the interval (pL , wH
∗
GL− (wH ) = GL (pL ). Remember that fraction ϕ > 0 of firms offer wages strictly below pL and fraction
∗ . Also remember that fraction ξ of low-ability workers accept
1 − η − ϕ ≥ 0 offer wages strictly above wH
∗ when offered (w ∗ , p ).
wH
H L
G0 , g1 , g2 , g3 , g5 and g6 satisfy the set of linear steady-state equations
g1 [φ + δ + ρ + λ(1 − ϕ)] = [φ + δ + λg5 ]ϕ ,
(36)
g2 [φ + δ + ρ + λ(1 − ϕ − η)] = [φ + δ + λ(g1 + g5 )]η(1 − ξ) ,
(37)
g3 [φ + δ + ρ + λ(1 − ϕ − η)] = [φ + δ + λ(g1 + g5 )]ηξ ,
(38)
G0 [φ + δ + ρ] = [φ + δ + λg5 ] + λg6 (1 − ϕ − η) ,
(39)
g5 [φ + δ + λ] = ρ(G0 − g1 − g2 ) ,
(40)
g6 [φ + δ + λ(1 − ϕ − η)] = ρ(g1 + g2 ) .
(41)
These can be solved for
g1 + g2 =
E − F (g1 + g2 )
C(E + ρ) + DE
, G0 =
,
B(E + ρ) + DF
E+ρ
with
B = (φ + δ + ρ + λ(1 − ϕ − η))(φ + δ + ρ + λ(1 − ϕ))(φ + δ + λ)
+λϕρ(φ + δ + ρ + λ(1 − ϕ − ηξ)) + λρη(1 − ξ)(φ + δ + ρ + λ(1 − ϕ)) ,
h
i
C = (φ + δ)(φ + δ + λ) (ϕ + η(1 − ξ))(φ + δ + ρ + λ(1 − ϕ)) − λϕηξ ,
h
i
D = λρ (ϕ + η(1 − ξ))(φ + δ + ρ + λ(1 − ϕ)) − λϕηξ ,
E = φ+δ+λ ,
ρλ(ϕ + η)
F =
.
φ + δ + λ(1 − ϕ − η)
The other variables gn , n = 1, . . . , 6 follow immediately from (36)–(41). The unemployment rate is
u = (φ + δ)/(φ + δ + λ). For the earnings distributions of initial wages, the steady state relations are
(φ + δ + λg5 )FL (w)
φ + δ + ρ + λ(1 − FL (w))
(φ + δ + λg5 )FH (w) + λg6 (FH (w) − ϕ − η)
GL (w) =
φ + δ + ρ + λ(1 − FH (w))
GL (w) =
if
w < pL ,
(42)
if
∗
w > wH
.
(43)
2. High-ability workers
For the distribution of initial wages, steady state relations yield
GH (w) =
(φ + δ)FH (w)
∗
, w 6= wH
,
φ + δ + ρ + λ(1 − FH (w))
and
∗
∗
∗
gH (wH
) = GH (wH
) − GH− (wH
)=
∗ ))η
(φ + δ + λGH− (wH
.
φ + δ + ρ + λ(1 − ϕ − η)
Profit Maximization
Firms are indifferent between all contracts in the offer distribution. In the following, we derive this
indifference relation for different wage offers to high-ability workers.
41
φ+δ+λg ∗ (b)
L
For convenience, we define α
ˆ≡α
, which is the ratio of low-ability worker who are either
φ+δ
unemployed or demoted at wage b, relative to the mass of unemployed high-ability workers.39 We also
define parameter A0 as in Section 3, equation (7).
1. wH ∈ [RH , w
˜H ): Firms offer separating contracts with slack incentive constraints.
When the firm offers wi to workers of ability i = H, L, profit is
Ω(wH , wL ) =
A0 [pL − wL ]
A0 [pH − wH ]
+α
ˆ
.
2
[φ + δ + ρ + λ(1 − FH (wH ))]
[φ + δ + ρ + λ(1 − FL (wL ))]2
With slack incentive constraints, profit is constant for both worker types independently. This gives rise
to the same wage offer distributions (8) as in the previous section. Rank preservation implies that the
two initial wages are linked according to (10), and the incentive constraint (6) implies that the threshold
wage w
˜H satisfies (11).
∗ ): Firms offer separating contracts with binding incentive constraints.
2. wH ∈ [w
˜H , wH
Incentive constraints are binding so that wL = w(w
ˆ H ) = wH − b + RL . The firm’s profit is
Ω(wH , w(w
ˆ H )) =
h
i
A0
p
−
w
+
α
ˆ
(p
−
w
+
b
−
R
)
.
H
H
L
H
L
(φ + δ + ρ + λ(1 − FH (wH )))2
The constant profit condition Ω(wH , w(w
ˆ H )) = Ω(RH , RL ) yields the wage offer distribution
"
#
pˆ − wH (1 + α
ˆ) + α
ˆ (b − RL ) 1/2
φ+δ+ρ+λ
∗
1−
FH (wH ) =
, wH ∈ [w
˜H , wH
),
ˆ
λ
pˆ − R
(44)
ˆ ≡ RH + α
where we define pˆ ≡ pH + α
ˆ pL and R
ˆ RL . We define
C(x) ≡
φ + δ + ρ + λ(1 − x)
,
φ+δ+ρ+λ
∗ )=F
and obtain, because of FH− (wH
L− (pL ) = ϕ, an equilibrium condition for ϕ
C(ϕ)2 =
pH − pL − b + RL
.
ˆ
pˆ − R
(45)
∗ : Mass η > 0 of firms offer the contract menu (w ∗ , p ). Fraction ξ > 0 of
3. wH = wH
H L
low-ability workers misreport their type.
These firm offer pL to low-ability workers of whom fraction 1 − ξ accept this contract so that firms
make zero profits on these workers. Fraction ξ of low-ability workers, being indifferent between the two
∗ = p + b − R and are demoted to wage b at the
contracts, report the wrong type, earn initial wage wH
L
L
firm’s learning rate ρ. On each worker of low ability hired into such a contract, the firm makes expected
profit
(φ + δ + λ)(RL − b) + ρ(pL − b)
∗
JL (wH
)=
.
(φ + δ + λ)(φ + δ + ρ + λ(1 − ϕ − η))
Note that low-ability workers before demotion quit at rate λ(1 − ϕ − η) since fraction 1 − ϕ − η of firms
∗ . After demotion, these workers quit at rate λ. Note also that J (w ∗ ) is
offer initial wages above wH
L
H
negative (see the proof of Lemma 3).
39
are
The mass α
φ+δ
φ+δ+λ
∗
φ+δ+λgL
(b)
φ+δ+λ
of low-ability workers are unemployed or employed at demotion wage b, whereas there
unemployed high-ability workers.
42
The rate at which low-ability workers are hired into this contract is
i
αλξ h
λˆ
αξ(φ + δ)(φ + δ + ρ + λ)
∗
hL (wH
)=
φ + δ + λ(gL∗ (b) + GL− (pL )) =
.
φ+δ+λ
(φ + δ + λ)[φ + δ + ρ + λ(1 − ϕ)]
The first expression is the flow of low-ability workers who are either unemployed or who are employed
at wages below pL who report the wrong type when meeting this firm (flow rate λξ). The second
expression makes use of the steady-state earnings distribution of low-ability workers (42). Therefore the
∗ is
firm’s profit on low-ability workers at wage wH
∗
∗
∗
ΩL (wH
) = hL (wH
)JL (wH
)=
A0 α
ˆ ξ[(φ + δ + λ)(RL − b) + ρ(pL − b)]
.
[φ + δ + ρ + λ(1 − ϕ)][φ + δ + ρ + λ(1 − ϕ − η)](φ + δ + λ)
∗ , quit at rate λ(1 − ϕ − η), and
Workers of high ability yield a profit flow before promotion pH − wH
λ(φ+δ)(φ+δ+ρ+λ)
. Thus, for the firm’s profit, we have a similar expression:
they are hired at rate (φ+δ+λ)(φ+δ+ρ+λ(1−ϕ))
∗
ΩH (wH
)=
∗ ]
A0 [pH − wH
.
[φ + δ + ρ + λ(1 − ϕ)][φ + δ + ρ + λ(1 − ϕ − η)]
∗ ) + Ω (w ∗ ) = Ω(R , R ) then implies
The constant-profit condition ΩL (wH
H
H
L
H
pH − pL − b + RL + ξ α
ˆ [RL − b +
C(ϕ)C(ϕ + η) =
ˆ
pˆ − R
ρ
φ+δ+λ (pL
− b)]
,
(46)
which is an equilibrium condition for the endogenous variable ξ.
∗ : Firms pool all workers in the same contract, promoting high-ability
4. wH > wH
workers and demoting low-ability workers.
If the equality
1−ϕ−η =0
(47)
∗ . Otherwise, positive mass 1 − ϕ − η of firms offer
holds, there are no firms offering wages above wH
∗ . These firms hire all low-ability workers who currently earn w ∗ or less, including those
wages wH > wH
H
low-ability workers who have been promoted to wage pL . Similar to the previous case, each worker of
low ability hired at wH yields negative profit
JL (wH ) =
(φ + δ + λ)(pL − wH ) + ρ(pL − b)
,
(φ + δ + λ)(φ + δ + ρ + λ(1 − FH (wH )))
since these workers quit at rate λ(1 − FH (wH )) (rate λ) before (after) demotion.
The rate at which low-ability workers are hired into this contract is
h
i
λα
hL (wH ) =
φ + δ + λ(gL∗ (b) + gL∗ (pL ) + GL (wH ))
φ+δ+λ
h
i
λα (φ + δ + ρ + λ)(φ + δ + λ(gL∗ (b) + gL∗ (pL ))) − λ2 gL∗ (pL )(ϕ + η)
=
.
(φ + δ + λ)[φ + δ + ρ + λ(1 − FH (wH ))]
The first expression is the flow of low-ability workers who are either unemployed or who are employed
at wages below wH meeting this firm. The second expression makes use of the steady-state earnings
distribution of low-ability workers (43). We define
ˆ
α
ˆ≡α
φ + δ + λ(gL∗ (b) + gL∗ (pL )) −
φ+δ
43
∗ (p )(ϕ+η)
λ2 g L
L
φ+δ+ρ+λ
,
∗ is
and find that the firm’s expected (negative) profit on low-ability workers at wages wH > wH
ΩL (wH ) = hL (wH )JL (wH ) =
ˆˆ [(φ + δ + λ)(pL − wH ) + ρ(pL − b)]
A0 α
.
[φ + δ + ρ + λ(1 − FH (wH ))]2 (φ + δ + λ)
For workers of high ability, the firm’s profit is
ΩH (wH ) =
A0 [pH − wH ]
.
[φ + δ + ρ + λ(1 − FH (wH ))]2
Now the constant-profit condition ΩL (wH ) + ΩH (wH ) = Ω(RH , RL ) yields the wage offer distribution

!1/2 
ρ
ˆ
ˆ
ˆ
p
ˆ
−
w
(1
+
α
ˆ
)
+
α
ˆ
(p
−
b)
H
L
φ+δ+ρ+λ
φ+δ+λ
∗
 , wH ∈ (wH
(48)
, wH ] ,
FH (wH ) =
1−
ˆ
λ
pˆ − R
ˆ
where we define pˆ
ˆ ≡ pH + α
ˆ pL . The top wage follows from FH (wH ) = 1:
wH =
1
h
ˆ
1+α
ˆ
pˆ
ˆ+
φ + δ + ρ 2
i
ˆˆ ρ
α
ˆ .
(pL − b) −
(ˆ
p − R)
φ+δ+λ
φ+δ+ρ+λ
∗ ) = lim
∗ FH (wH ) =
Since the distribution of wage offers must have connected support, FH+ (wH
wH &wH
ϕ + η, we obtain an implicit condition for variable η:
ˆˆ [RL − b +
pH − pL − b + RL + α
C(ϕ + η) =
ˆ
pˆ − R
2
ρ
φ+δ+λ (pL
− b)]
.
(49)
Reservation Wages
It remains to derive reservation wages for the two workers types. For both types, we make use of
(32) and calculate the difference Vi (pi ) − Ui .
For workers of low ability we have from (19) and (21)
Z wH
(φ + δ)VL (pL ) = pL + δUL + λ
[VLH (w) − VL (pL )] dFH (w) ,
(50)
∗
wH
Z
wH
[max[VLL (w(w)),
ˆ
VLH (w)] − UL ] dFH (w)
φUL = b + λ
RH
Z →w∗
H
= b+λ
Z
[VLL (w(w))
ˆ
− UL ] dFH (w)
RH
wH
+λ
∗
wH
Z
[VLH (w) − VL (pL ) + VL (pL ) − UL ] dFH (w)
∗
→wH
= b+λ
Z
(51)
[VLL (w(w))
ˆ
− UL ] dFH (w)
RH
wH
+λ
∗
wH
[VLH (w) − VL (pL )] dFH (w) + λ(1 − ϕ)[VL (pL ) − UL ] .
Subtracting (51) from (50) and substitution into (32) gives
Z →w∗
H
φ + δ + λ(1 − ϕ)
(b − RL ) = pL − b − λ
[VLL (w(w))
ˆ
− UL ] dFH (w) .
ρ
RH
44
(52)
The integral expression in this equation can be calculated as follows:
Z →w∗
Z →pL
H
λ
VLL (w(w))
ˆ
− UL dFH (w) = λ
[VLL (w) − VLL (RL )] dFL (w)
RH
RL
Z
pL
=
RL
2C(ϕ)2
λ[ϕ − FL (w)]
dw
φ + δ + ρ + λ(1 − FL (w))
2C(ϕ)
[pH − RH − pL + RL ]1/2 [pH − pL − b + RL ]1/2 .
1+α
ˆ
1+α
ˆ
The last equation makes use of (8), (44), and FL (w) = FH (w + b − RL ) for wL ≥ w
˜L = w˜H − b + RL ,
similar to the calculations in the proof of Proposition 1. Substitution back into (52) yields an equation
which defines RL implicitly.
For workers of high ability, we obtain a similar reservation wage equation:
Z wH
φ+δ
(b − RH ) = pH − b − λ
[VHH (w) − UH ] dFH (w) .
(53)
ρ
RH
= (pL − RL )(1 − 2C(ϕ)) +
ˆ −
(ˆ
p − R)
For the integral expression, we obtain
Z wH
Z
[VHH (w) − VHH (RH )]dFH (w) =
RH
∗
→wH
∗
[VHH (w) − VHH (RH )] dFH (w) + η[VHH (wH
) − VHH (RH )]
RH
wH
Z
+
∗
→wH
Z
∗
wH
=
RH
Z
∗
wH
=
RH
∗
∗
) − VHH (RH )]
[VHH (w) − VHH (wH
)]dFH (w) + (1 − ϕ − η)[VHH (wH
Z wH
ϕ − FH (w)
1 − FH (w)
dw +
dw
∗
φ + δ + ρ + λ(1 − FH (w))
φ + δ + ρ + λ(1 − FH (w))
wH
Z w∗
H
1−ϕ
dw
+
RH φ + δ + ρ + λ(1 − FH (w))
Z wH
1 − FH (w)
1 − FH (w)
dw +
dw .
∗
φ + δ + ρ + λ(1 − FH (w))
φ + δ + ρ + λ(1 − FH (w))
wH
Using (8), (44) and (48), the sum of the last two integrals can be further calculated to obtain
Z wH
2C(1)C(ϕ)
ˆ
λ
[VHH (w) − VHH (RH )]dFH (w) = wH − RH − 2C(1)(pH − RH ) +
(ˆ
p − R)
1+α
ˆ
RH
2C(1)ˆ
α
2C(1)(C(1) − C(ϕ + η))
ˆ .
[pH − pL − RH + RL ]1/2 [pH − b − pL + RL ]1/2 +
(ˆ
p − R)
ˆˆ
1+α
ˆ
1+α
Substitution back into (53) yields the implicit equation for RH .
This completes the first part of the proof, namely the derivation of all equilibrium conditions.
Equilibrium Existence
There are two types of candidate equilibria in simple contracts. The first case is that the mass point
∗ = w
at wH
H is the highest offered initial wage. In this case the equilibrium variables (ϕ, ξ, η, RL , RH )
∗ in
satisfy equations (45), (46), (47), (52) and (53). Second, some firms offer initial wages above wH
which case (ϕ, ξ, η, RL , RH ) satisfies (45), (46), (49), (52) and (53) (so that η < 1 − ϕ). Typically the
second case describes an equilibrium if the learning rate falls below some threshold ρ3 . If this threshold
value exists, both (47) and (49) are jointly satisfied at ρ = ρ3 .
+
45
To prove equilibrium existence, we apply Brouwer’s fixed-point theorem by defining a suitable continuous map H : X → X on a compact, convex subset X ⊂ IR5 , such that every fixed point of H
satisfies the equilibrium conditions. First, we define upper and lower bounds on reservation wages. For
workers of high ability, note that the integral on the right-hand side of (53) is bounded below by zero
and it is bounded above by
Z
Z
pH − b − λ
[VHH (w) − UH ] dFH (w)
pH − φUH
RH
[VHH (w) − UH ] dFH (w) <
=
,
φ+δ
φ+δ
R
H
which implies
Z
[VHH (w) − UH ] dFH (w) <
RH
pH − b
.
φ+δ+λ
Therefore, (53) defines upper and lower bounds on RH :
ρ
ρ
RH ≡ b −
(p − b) < RH < RH ≡ b −
(p − b) .
φ+δ H
φ+δ+λ H
For workers of low ability, the integral on the right-hand side of (52) is bounded below by zero which
defines the lower bound
ρ
ρ
RL > b −
(p − b) ≥ RL ≡ b −
(p − b) .
φ+δ L
φ + δ + λ(1 − ϕ) L
The integral in (52) is bounded above by
Z →w∗
H
ϕ(b − RL )
[VLL (w(w))
ˆ
− UL ] dFH (w) < ϕ[VL (pL ) − UL ] =
,
ρ
RL
which defines the upper bound
RL < RL ≡ b −
ρ
(p − b) .
φ+δ+λ L
We can now define
o
n
X ≡ (ϕ, ξ, η, RL , RH ) ∈ [0, 1]3 × [RL , RL ] × [RH , RH ] , η + ϕ ≤ 1 ,
which is a compact, convex subset of IR5 .
Define RHS(N ) (LHS(N )) for the right-hand side (left-hand side) of generic equation (N), and define
functions Gi : X → IR by
G1 (ϕ, ξ, η, RL , RH ) = LHS(45) − RHS(45) ,
G2 (ϕ, ξ, η, RL , RH ) = LHS(46) − RHS(46) ,
G3 (ϕ, ξ, η, RL , RH ) = LHS(49) − RHS(49) ,
G4 (ϕ, ξ, η, RL , RH ) = LHS(52) − RHS(52) ,
G5 (ϕ, ξ, η, RL , RH ) = LHS(53) − RHS(53) .
Since all steady-state measures and the other expressions defined above depend continuously on (ϕ, ξ, η, RL , RH ),
functions Gi are continuous. Then define the map H : X → X by
H1 (x) = max{0, min{1, ϕ + G1 (x)}} ,
H2 (x) = max{0, min{1, ξ − G2 (x)}} ,
H3 (x) = max{0, min{1 − ϕ, η + G3 (x)}} ,
H4 (x) = max{RL , min{RL , RL + G4 (x)}} ,
H5 (x) = max{RH , min{RH , RH + G5 (x)}} ,
46
for any x = (ϕ, ξ, η, RL , RH ) ∈ X. It is obvious that H maps X into itself and that it is continuous.
∗ , R∗ ) ∈ X. It still needs to be shown that this
Hence it has a fixed-point, denoted x∗ = (ϕ∗ , ξ ∗ , η ∗ , RL
H
fixed-point is a candidate equilibrium. For this we need to prove that Gi (x∗ ) = 0 for i = 1, 2, 4, 5, and
that G3 (x∗ ) ≥ 0 if η ∗ + ϕ∗ = 1.
To show G1 (x∗ ) = 0, we have to prove that ϕ∗ ∈ (0, 1). Observe that, due to Proposition 1, ρ < ρ2
is equivalent to wH > pL + b − RL , with wH defined in (17). This is equivalent to
C(1)2 <
pH − pL + RL − b
.
p−R
(54)
ˆ = R. Then (54) implies that
Hence, at ϕ = 1, we have that gL∗ (b) = 0, α
ˆ = α, so that pˆ = p, R
LHS(45) < RHS(45) at ϕ = 1 provided that ρ < ρ2 . Now suppose that ϕ∗ = 1, so that G1 (x∗ ) < 0.
But this contradicts H1 (x∗ ) = ϕ∗ = 1. Second, suppose that ϕ∗ = 0, so that LHS(45) = 1 while
RHS(45) < 1, and hence G1 (x∗ ) > 0, which contradicts H1 (x∗ ) = ϕ∗ = 0.
Next we show that η ∗ > 0 and that G3 (x∗ ) ≥ 0, ϕ∗ + η ∗ ≤ 1 hold with complementary slackness.
ρ
Suppose first that η ∗ = 0. Then, since G1 (x∗ ) = 0 and because of [RL − b + φ+δ+λ
(pL − b)] < 0 (proof
of Lemma 1),
pH − pL − b + RL
C(ϕ∗ )2 =
> RHS(49) .
ˆ
pˆ − R
This implies G3 (x∗ ) > 0, which contradicts H3 (x∗ ) = η ∗ = 0. From H3 (x∗ ) = η ∗ it is also easy to show
that G3 (x∗ ) ≥ 0 and that η ∗ + ϕ∗ ≤ 1. Moreover, one of these inequalities must bind if H3 (x∗ ) = η ∗ .
To prove G2 (x∗ ) = 0, we have to show that ξ ∗ ∈ (0, 1). Suppose first that ξ ∗ = 0; then, because of
G1 (x∗ ) = 0 and η ∗ > 0,
C(ϕ∗ )C(ϕ∗ + η ∗ ) < C(ϕ∗ )2 =
pH − pL − b + RL
= RHS(46) ,
ˆ
pˆ − R
so that G2 (x∗ ) < 0. This contradicts H2 (x∗ ) = ξ ∗ = 0. Now suppose ξ ∗ = 1, which implies gL∗ (pL ) = 0
ˆ
and therefore α
ˆ=α
ˆ . This implies that
RHS(46) = RHS(49) ≤ C(ϕ∗ + η ∗ )2 < C(ϕ∗ )C(ϕ∗ + η ∗ ) ,
because of η ∗ > 0 and G3 (x∗ ) ≥ 0. Hence G2 (x∗ ) > 0, which contradicts H2 (x∗ ) = ξ ∗ = 1.
Finally, it is straightforward to show that G4 (x) < 0 (G5 (x) < 0) if RL = RL (RH = RH ) and that
G4 (x) > 0 (G5 (x) > 0) if RL = RL (RH = RH ). This proves that Gi (x∗ ) = 0 for i = 4, 5.
This completes the proof of Proposition 2.
2
Lemma A.2: In a Burdett-Mortensen (1998) model with matching rates λ0 and λ1 for unemployed
and employed workers, separation rate δ, birth/death rate φ, let Gi denote the earnings distribution of
workers who had i ≥ 0 job-to-job transitions since the last unemployment spell. Then Gi first-order
stochastically dominates Gj for any i > j. Hence a worker’s expected wage is increasing in the number
of job-to-job transitions since the last unemployment spell.
Proof: Write F for the wage-offer distribution with support [R, w] where R is the reservation wage.
Let ei be the mass of employed workers with exactly i job-to-job transitions since the last unemployment
spell, and let u be the mass of unemployed workers. Let Gi (w) be the earnings distribution of workers
in group ei , and write gi for the density.
For group ei Gi (w), i ≥ 1, the outflow=inflow condition is
Z w
Z w
h
i
ei (Φ + δ)Gi (w) + λ1
gi (w0 )[1 − F (w0 )]dw0 = ei−1 λ1
gi−1 (w0 )[F (w) − F (w0 )]dw0 .
(55)
R
R
47
For group e0 G0 (w), the corresponding condition is
Z w
i
h
g0 (w0 )[1 − F (w0 )]dw0 = uλ0 F (w) .
e0 (Φ + δ)G0 (w) + λi
(56)
R
Partial integration and differentiation yields the following formulas for the densities:
gi (w) =
g0 (w) =
λ1 ei−1 Gi−1 (w)
f (w)ψ(w) , i ≥ 1 ,
ei
λ0 u f (w)ψ(w) ,
e0
with ψ(w) ≡ [Φ + δ + λ(1 − F (w))]−1 . Because ψ(w) is strictly increasing, it first follows that
g0 (w)/f (w) ≈ ψ(w) is strictly increasing. Hence G0 likelihood-ratio dominates F . Second, since g0 (w)
is proportional to f (w)ψ(w), it follows that g1 (w)/g0 (w) ≈ G0 (w) is strictly increasing. Hence, G1
likelihood-ratio dominates G0 , which in turn implies reverse-hazard-rate dominance: g1 (w)/G1 (w) ≥
g0 (w)/G0 (w) (see Krishna (2009)). Third, it follows recursively that any Gi likelihood-ratio dominates
Gi−1 for i ≥ 2. To see this, consider
e2 G (w)
gi (w)
= i−1 i−1
.
gi−1 (w)
ei ei−2 Gi−2 (w)
Here the right-hand side is increasing iff gi−1 (w)Gi−2 (w) ≥ gi−2 (w)Gi−1 (w) for all w which is true iff
Gi−1 reverse-hazard-rate dominates Gi−2 which is true if Gi−1 likelihood-ratio dominates Gi−2 . As this
is true for i = 2, it holds for all i > 2 by induction. It follows that any Gi first-order stochastically
dominates Gj for i > j (Krishna (2009)).
2
48
Appendix C: Data and Simulations
Our discussion in Section 4.1 extends the work of Light and McGarry (1998) by considering a worker’s
cumulative count of the number of job-to-job transitions and cumulative count of the number of nonemployment spells. To do so, we use the National Longitudinal Survey of Youth 1979 (NLSY), focusing
on white male and female workers. Following Light and McGarry (1998), we drop from this group those
workers with indeterminate entry dates, those with entry dates that preceded their 16th birthday or
01/01/78 (the earliest date included in our regressions timeframe), those who stayed in school throughout
1979-1993, those who were observed for less than 8 years after their entry date and those without
employment data during the 1979-1993 period. Also following Light and McGarry (1998), to determine
the entry date we use as a guide the start of the first non-enrolment (in education) spell lasting more
than 12 months. Because of the lack of detailed enrolment information for the survey years 1979-1980,
we use a different method in those years relative to the 1981-2010 survey years. In the 1979-1980 survey
years, the NLSY only provides information on the date last enrolled. For these two years, we use the
number of months between the date last enrolled and the interview date, and identify the entry date
for those who had 12 months in between. From 1981 onwards, the NLSY provides a dummy variable
for each month since the last interview which is equal to 1 if the respondent was enrolled in that month
and zero otherwise. In this case we use the first 12-months non-enrolled streak and took the first month
of that streak as the entry month.
An important difference with Light and McGarry (1998) is that we create a “main job” dummy
variable for a particular month to compute transitions, instead of using all of the overlapping jobs the
worker could have held in the same month. In particular, for months where more than one job was held,
we follow these tie-breaking rules: (i) The job that had the most hours worked per week is taken to be
the main job. (ii) If there were two or more jobs that month with the same maximum hours, the job
that began earlier (earlier “jobstart”) is chosen as the main job. (iii) If two or more jobs that month
had the same maximum hours and “jobstart”, then the one with higher wages is chosen as the main job.
(iv) If two or more jobs had the same hours, start and wages, then the one which lasted longer (later
“jobstop”) is considered the main job. (v) If there were still two jobs that had the same hours, start, stop
and wages, we assume these to be exactly the same jobs, in which case we choose arbitrarily the one
with a smaller job id. Job-to-job transitions are then computed by identifying the months for which the
main job changed such that the time gap between these jobs is less than a month. The non-employment
spell variable is created when the main job variable is either missing or zero.
Using this data set, we take the same econometric specification proposed by Light and McGarry
(1998), except that instead of including the total number of job separations at 2 years and 8 years as
regressors, we replace them by the cumulative counts of the numbers of job-to-job transitions and nonemployment spells. Other regressors include a quadratic on actual experience and a quadratic on tenure,
years of schooling, marital status dummy, health status dummy, a part-time/full-time employment
dummy, a government sector dummy, a union job dummy, one-digit industry dummies, unemployment
rate and wage index as measures of aggregate conditions, a dummy if the individual lived in a city, a
dummy if the individual lived in the South and a gender dummy. The dependent variable is the real log
hourly wage. All these variables are computed following Light and McGarry (1998).
We then run the OLS and IV regressions considered by these authors, using their same error structure
and procedure for the IV regressions. The only difference is that we use the cumulative numbers of jobto-job transitions and non-employment spells as part of the IV procedure. We perform these regressions
considering all available years (1979-2010), all years up to 1994 and all years up to 1989 in the NLSY.
We also perform these regressions considering the first 15 years of workers’ labor market histories,
the first 10 years of workers’ labor market histories and the first 8 years of workers’ labor market
histories. Further, following Light and McGarry (1998) we consider different specifications for the error
49
structure in the IV regressions. We first consider the case in which the error structure only captures
the effects of time-invariant individual characteristics. We then consider the cases in which the error
structure considers the individual and match-specific effects together in the error term. Table 3 presents
the results. We obtain a positive coefficient on the cumulative number of job-to-job transitions when
considering only individual characteristics and when considering individual characteristics in conjunction
with match-specific characteristics. Finally, to make sure we indeed follow the same procedure as Light
and McGarry (1998), we replicate their original exercise, using separately all jobs and the main jobs,
and obtain very similar results.
In the main text, Table 2 reports the estimates using the OLS regressions without the tenure variable.
See Table 4 for the full regression result under this specification. The reason we present the regressions
results without tenure in Table 2 is because in all our simulations we find that the Burdett and Mortensen
(1998) model has a very strong positive relationship between wages and labor market experience, but
not necessarily between wages and tenure. In particular, returns to tenure turn negative when the
displacement shock, δ, becomes sufficiently high. With small enough δ and φ shocks, the Burdett and
Mortensen (1998) model generates an aggregate positive relationship between wages and tenure because
workers in high-paying jobs stay in those jobs for a long time. However, when δ shocks become more
frequent, including our benchmark value of δ = 0.02, workers that climb the wage ladder and end up in
high-paying jobs are not able to stay in those jobs for a long time. In these cases we observe a negative
relationship between tenure and wages (see Manning (2003) -Appendix 6A- for a formalization of this
argument using a partial equilibrium set up). Nevertheless, even if we include a quadratic on tenure
in the Burdett and Mortensen (1998) simulated regressions, the same general conclusion drawn from
Table 2 holds.
Finally the regressions for the Burdett-Mortensen (B-M) model and for our (CT-K) model reported
in Table 2 are based on simulations of 100,000 workers who we follow for up to 30 years, where all
Poisson shocks (matching, separation, learning, exit) arrive at monthly frequency. We also run the same
regressions following workers for the first 15, 10 and 8 years of workers’ labor market histories (as also
done in the data) and find that our results do not qualitatively change. Note that for these simulations
we make sure that we generate the same data format as in the NLSY. Further, Table 5 reports the
average cumulative counts of job-to-job transitions (JTJ) and non-employment spells (NESP) as well
as workers’ actual experience (EXP), job duration (J-DUR) and non-employment duration (NE-DUR)
implied by the NLSY data and the (B-M) and (CT-K) simulated data sets we use for Table 2. Both
our model and the calibrated B-M model fit these data averages rather well.
50
51
0.0338***
-0.0057***
0.0211***
-0.0058***
0.0005
-2.23E-05
-0.2942***
-0.1951***
0.2528***
0.3516***
-0.0746***
0.0625***
0.0194**
-0.1204***
-0.0196***
-0.2821***
0.1194***
0.0518***
-0.0372***
-0.0009
0.0312***
-0.6141***
-0.1782***
-0.1449***
-0.2269***
-0.1372***
-0.3961***
0.1325***
-0.3257***
0.1704***
1.6531***
57,047
0.3071
0.3067
Years of work experience X
X 2 /10
Years of job tenure T
T 2 /10
Transitions * T
Transitions * T 2
1 if <12 years of schooling
1 if 12 years of schooling
1 if 16 years of schooling
1 if ≥ 17 years of schooling
1 if in school
1 if married
1 if divorced
1 if has health limitations
1 if works < 35 hrs/wk
1 if government job
1 if union job
1 if lives in city
1 if lives in the south
Unemp rate
Log wage index
1 if agriculture
1 if mining
1 if construction
1 if manufacturing
1 if transportation
1 if wholesale & retail
1 if info, finance & insurance
1 if services
1 if male
Constant
Obs
R2
Adj R2
Num of caseid
Num of indivjob
4,538
57,047
0.2687
-0.2380***
-0.1774***
0.2311***
0.2326***
-0.1181***
0.0548***
0.0236**
-0.0687***
0.0181**
-0.1650***
0.1344***
0.0092*
-0.0297***
-0.0032***
0.0439***
-0.3367***
-0.0186
-0.0232
-0.0751***
-0.0671***
-0.2368***
-0.0439**
-0.2085***
0.1694***
1.5094***
0.0300***
-0.0051***
0.0234***
-0.0066***
-0.0020***
0.0009***
0.0258***
-0.0578***
20,325
57,047
0.2810
-0.2302***
-0.1684***
0.2443***
0.2733***
-0.0810***
0.0597***
0.0110
-0.0928***
0.0481***
-0.2070***
0.1514***
0.0153***
-0.0251***
-0.0006
0.0327***
-0.4472***
-0.0209
-0.0597**
-0.1175***
-0.0943***
-0.3220***
-0.0257
-0.2587***
0.1753***
1.4840***
0.0268***
-0.0043***
0.0169***
-0.0050***
-0.0014**
0.0007***
0.0251***
-0.0287***
All years
IV/GLS
WE
WME
42,604
0.3445
0.3440
-0.2663***
-0.1769***
0.2410***
0.3700***
-0.0593***
0.0310***
0.0192*
-0.0967***
0.0023
-0.1458***
0.1557***
0.0818***
-0.0268***
-0.0085***
0.0017
-0.4483***
0.0175
0.0089
-0.0853***
-0.0063
-0.2536***
-0.0251
-0.1847***
0.1456***
1.6905***
0.0471***
-0.0119***
0.0390***
-0.0203***
0.0002
0.0002
-0.0036***
-0.0114***
OLS
4,519
42,604
0.3093
-0.1935***
-0.1163***
0.2460***
0.3268***
-0.1033***
0.0326***
0.0152
-0.0300**
0.0386***
-0.0566***
0.1642***
0.0214***
-0.0246**
-0.0130***
0.0221***
-0.2169***
0.0850**
0.0670***
0.0039
0.0058
-0.1519***
0.0210
-0.1247***
0.1601***
1.5935***
0.0370***
-0.0056***
0.0390***
-0.0236***
-0.0043***
0.0030***
0.0183***
-0.0514***
16,744
42,604
0.3269
-0.1783***
-0.1144***
0.2454***
0.3026***
-0.0656***
0.0340***
0.0004
-0.0553***
0.0576***
-0.0911***
0.1703***
0.0364***
-0.0200***
-0.0101***
0.0071
-0.3471***
-0.1059**
0.0394
-0.0354
0.0023
-0.2279***
0.0394
-0.1636***
0.1594***
1.5677***
0.0372***
-0.0066***
0.0318***
-0.0197***
-0.0028***
0.0020***
0.0161***
-0.0137***
First 15 years
IV/GLS
WE
WME
33,833
0.3320
0.3314
-0.2667***
-0.1722***
0.2298***
0.3467***
-0.0431***
0.0218***
0.0271**
-0.1071***
-0.0111
-0.1227***
0.1590***
0.0745***
-0.0254***
-0.0057***
0.0068
-0.4327***
0.0732**
0.0563***
-0.0580***
0.0347
-0.2219***
-0.0127
-0.1733***
0.1366***
1.5773***
0.0566***
-0.0193***
0.0454***
-0.0296***
-0.0001
0.001
-0.0029**
-0.010***
OLS
4,498
33,833
0.2929
-0.1711***
-0.1081***
0.2303***
0.3082***
-0.0885***
0.0309***
-0.0165
-0.0279*
0.0262***
-0.0339**
0.1695***
0.0230***
-0.0232**
-0.0105***
0.0233***
-0.2145***
0.1140***
0.0941***
0.0213
0.0336
-0.1286***
0.0340
-0.1229***
0.1521***
1.5034***
0.0284**
0.0029
0.0599***
-0.0523***
-0.0092***
0.0097***
0.0261***
-0.0484***
14,629
33,833
0.3183
-0.1672***
-0.1144***
0.2314***
0.2805***
-0.0471***
0.0291***
-0.0043
-0.0598***
0.0423***
-0.0625***
0.1687***
0.0419***
-0.0207**
-0.0059***
0.0075
-0.3396***
0.1383***
0.0713**
-0.0172
0.0427
-0.1928***
0.0448
-0.1558***
0.1519***
1.4332***
0.0588***
-0.0200***
0.0428***
-0.0407***
-0.0034
0.0041
0.0123***
-0.0065
First 10 years
IV/GLS
WE
WME
28,212
0.3447
0.3439
-0.2596***
-0.1655***
0.2248***
0.3450***
-0.0371***
0.0178***
0.0187
-0.1130***
-0.0170**
-0.1257***
0.1616***
0.0672***
-0.0181***
-0.0056***
0.0200***
-0.4383***
0.1065***
0.0585***
-0.0481**
0.0375*
-0.2136***
-0.0351
-0.1769***
0.1263***
1.4833***
0.0581***
-0.0224***
0.0490***
-0.0341***
0.001
-0.0019
-0.0022*
-0.0098***
OLS
4,473
28,212
0.3134
-0.1726***
-0.1159***
0.2329***
0.3309***
-0.0842***
0.0223***
-0.0018
-0.0411***
0.0206**
-0.0430***
0.1643***
0.0251***
-0.0145
-0.0100***
0.0369***
-0.2514***
0.1504***
0.0899***
0.0217
0.0397
-0.1290***
0.0082
-0.1328***
0.1406***
1.4265***
0.0263**
0.0130
0.0672***
-0.0757***
-0.0085
0.0100
0.0168
-0.0461***
13,198
28,212
0.3287
-0.1541***
-0.1141***
0.2226***
0.2787***
-0.0392***
0.0210***
-0.0080
-0.0606***
0.0445***
-0.0690***
0.1674***
0.0419***
-0.0127
-0.0049***
0.0174***
-0.3431***
0.1664***
0.0792**
-0.0080
0.0508
-0.1781***
0.0268
-0.1580***
0.1410***
1.3117***
0.0731***
-0.0308**
0.0606***
-0.0759***
-0.0030
0.0041
0.0079
-0.0020
First 8 years
IV/GLS
WE
WME
Error tern including time-invariant worker and match-specific heterogeneity.
*** p<0.01, ** p<0.05, * p<0.1. Sample: Male and female white individuals. Dependent variable: log real hourly wage. WE: Error term including only time-invariant worker heterogeneity. WME:
-0.0040***
-0.0154***
OLS
Job-to-job transitions
Non-employment spells
VARIABLES
Table 3: OLS and IV regressions with cumulative job-to-job transitions and non-employment spells
Table 4: OLS regressions without tenure
All years
First 15 years
First 10 years
First 8 years
Job-to-job transitions
Non-employment spells
-0.0073***
-0.0185***
-0.0081***
-0.0159***
-0.0075***
-0.0140***
-0.0070***
-0.0137***
Years of work experience X
X 2 /10
0.0431***
-0.0075***
0.0657***
-0.0190***
0.0792***
-0.0300***
0.0835***
-0.0360***
1 if <12 years of schooling
1 if 12 years of schooling
1 if 16 years of schooling
1 if ≥ 17 years of schooling
1 if in school
1 if married
1 if divorced
1 if has health limitations
1 if works < 35 hrs/wk
1 if government job
1 if union job
1 if lives in city
1 if lives in the south
Unemp rate
Log wage index
1 if agriculture
1 if mining
1 if construction
1 if manufacturing
1 if transportation
1 if wholesale & retail
1 if inf, finance & insurance
1 if services
1 if male
Constant
-0.3036***
-0.1931***
0.2653***
0.3688***
-0.0872***
0.0698***
0.0184*
-0.1166***
-0.0396***
-0.2487***
0.1341***
0.0500***
-0.0362***
-0.001
0.0331***
-0.5755***
-0.1473***
-0.1228***
-0.2008***
-0.1151***
-0.3607***
-0.1164***
-0.3198***
0.1707***
1.6476***
-0.2721***
-0.1807***
0.2520***
0.3868***
-0.0596***
0.0349***
0.0146
-0.0949***
-0.0162***
-0.1433***
0.1641***
0.0820***
-0.0310***
-0.0089***
0.0057
-0.4434***
0.009
0.0011
-0.0855***
-0.0102
-0.2573***
-0.0299*
-0.1902***
0.1516***
1.7072***
-0.2726***
-0.1748***
0.2422***
0.3659***
-0.0426***
0.0242***
0.0210
-0.1040***
-0.0281***
-0.1183***
0.1636***
0.0751***
-0.0299***
-0.0055***
0.0087
-0.4283***
0.0620*
0.0509**
-0.0570***
0.0327
-0.2234***
-0.0166
-0.1767***
0.1423***
1.5934***
-0.2658***
-0.1683***
0.2372***
0.3646***
-0.0359***
0.0197***
0.0113
-0.1096***
-0.0336***
-0.1208***
0.1656***
0.0674***
-0.0224***
-0.0051***
0.0230***
-0.4301***
0.0980***
0.0558**
-0.0452**
0.0376*
-0.2123***
-0.0370*
-0.1777***
0.1311***
1.4874***
Obs
R2
62,269
0.3309
42,604
0.339
33,833
0.3275
28,212
0.3415
VARIABLES
*** p<0.01, ** p<0.05, * p<0.1. Sample: Male and female white individuals. Dependent variable: log real
hourly wage.
52
Table 5: Data and model averages
Means
Data
JTJ
NESP
EXP
J-DUR
NE-DUR
4.2
3.9
11.6
2.3
0.87
53
Models
B-M CT-K
3.7
3.3
3.6
3.6
10.8
10.9
3.4
2.5
0.69
0.68
Appendix D: Offers Contingent on Employment Status
In this Appendix we fully characterize the equilibrium when firms condition their up-or-out contracts on
employment status. We first present workers value functions. Then we prove that the offer distributions
faced by unemployed and employed workers do not have overlapping supports. Finally, we characterize
the equilibrium. The arguments used here can then be used to analyze the equilibrium when firms
condition their up-or-down contracts on employment status.
Workers Value Functions: It is convenient to think of workers randomly meeting firms who draw
s from distribution F s and who offer w s = w
s ) to low-ability workers.
the high-ability wage offer wH
ˆ s (wH
H
L
This implies that the value of unemployment is given by
Z wu
H
max[ViL (w
ˆ u (x)) − Ui , ViH (x) − Ui , 0]dFHu (x) .
(57)
φUi = b + λ
wu
H
The value of employment at initial wage w for a worker of ability i that reported truthfully his type is
given by
Z we
H
φVii (wi ) = wi + λ
max[ViL (w
ˆ e (x)) − Vii (wi ), ViH (x) − Vii (wi ), 0]dFHe (x)
e
(58)
wH
+δ(Ui − Vii (wi )) + ρ(Vi (pi ) − Vii (wi )) ,
where the continuation value after promotion is given by (21) with FHe . The value of employment of a
worker of type i that misreported his type and is currently earning the initial wage wj is given by
Z
φVij (wj ) = wj + λ
weH
weH
max[ViL (w
ˆ e (x)) − Vij (wj ), ViH (x) − Vij (wj ), 0]dFHe (x)
+(δ + ρ)(Ui − Vij (wj )) .
The incentive-compatibility constraint is given by wjs − wis ≤ ρ[Vi (pi ) − Ui ].
Proof of Lemma 4: To show this, it is useful to note that in any equilibrium wei > wui ≥ Ri . This
follows since, for example, wei < wui implies firms offering wei will not hire any worker and will make
positive profits by offering a wage slightly above wui . We divide the proof in two steps. The first step
constructs the profits of firms when hiring unemployed workers and derives some preliminary results.
The second step compares the firms’ profits when hiring employed workers under the assumption of
overlapping supports.
Step 1:
u and w u = w
u ) to unemployed workers. Note that this firm could
Consider a firm offering wH
ˆ u (wH
L
u = w u , while when it separates
be separating or pooling workers. When this firm pools we have that wH
L
u
u
u
u
u
u ) + Ωu (w u ), where
workers wH 6= wL . In either case its steady-state profit is Ω (wH , wL ) = ΩuH (wH
L
L
Ωui (wiu ) =
λui αi (pi − wiu )
u )) ,
φ + δ + ρ + λ(1 − FHe (wH
(59)
for i = L, H. Let Niu (wiu ) denote the mass of workers hired from unemployment of ability i = L, H
earning an initial wage no greater than wiu . Steady state turnover implies that
Niu (wiu ) =
λui αi Fiu (wiu )
u )) .
φ + δ + ρ + λ(1 − FHe (wH
54
Now we show under what conditions firms would prefer to offer separating contracts when hiring unemployed workers. First, if satisfying the incentive-compatibility constraint of low-ability workers implies
u > w u and w u ≤ p for i = L, H, this firm will strictly prefer to separate workers. To verify this
wH
i
i
L
0
claim, suppose this firm offered a wage wLu to low-ability workers that did not satisfy their incentive
u constant. (59) then implies this firm will strictly reduce its profits by
constraint, while keeping wH
doing so, as it will hire low-ability workers at a higher wage while keeping the hiring and retention rates
u ≤ w u , but w u < R , this firm will
constant. Second, if satisfying incentive compatibility implies wH
L
L
H
u
also prefer to separate workers, as offering wH to all unemployed workers will only hire high-ability
u ≤ w u , but w u ≥ R , then this firm
workers. However, if satisfying incentive compatibility implies wH
L
L
H
u
prefers to pool workers and offer both types wH .
Also note that wei > wui ≥ Ri and (59) implies that in equilibrium wui = Ri and firms separate
workers at low wages. Further, (59) also implies that any firm offering wages wiu ∈ [wui , wei ) for each
i = L, H, must offer wiu = Ri , as this firm faces a constant hiring rate and all workers employed in this
firm quit as soon as they get an outside offer.
Finally note that in equilibrium wei ≥ wui for i = L, H. To verify this argument fix wei for i = L, H
and suppose wei < wui for i = L, H. Note that (59) then implies that the firm offering (wuL , wuH ) will
optimally set wui = wei for i = L, H, since by doing so it increases flow profits while keeping constant its
hiring and retention rates. Reducing the wui below wei will be optimal, for example, when in equilibrium
wei > wui for i = L, H.
Step 2:
In this step we prove the non-overlapping support result by contradiction. Suppose there exists an
equilibrium in which wui ∈ (wei , wei ] for i = L, H. We want to show that wui > wei violates the constantprofit condition in the employed workers’ market and hence cannot occur in any equilibrium. To do so
consider a firmP
offering wages wie = wei for i = L, H. This firm’s steady-state profit is then given by
Ωe (weH , weL ) = i=L,H Ωei (wei ), where
Ωei (wei ) =
λFiu (Ri )
λNiu (wei )[pi − wei ]
=
Ωu (Ri ) .
φ+δ+ρ+λ
φ+δ+ρ+λ i
(60)
The second equality follows from noting that this firm only hires workers that are currently earning
Ri , and it maximises profits by setting wei = Ri + ε, where ε > 0 is sufficiently small, for i = L, H.
Continuity of (59) then implies Ωui (Ri ) = Ωui (wei ). These results also imply that a firm offering wei for
i = L, H will separate workers in equilibrium.
e = w u + ε ≤ p to employed workers. Here we have several
Now consider a firm offering a wage wH
H
H
possible cases depending on whether the firms decide to pool or separate when hiring unemployed and
employed workers. Note that firms could follow different strategies when hiring workers of different
employment status.
First assume that the incentive constraint of low-ability workers is binding at wuH , such that wuL =
e = w u +ε ≤ p to employed
wuH −ρ(pL −φUL )/(φ+δ), and suppose that wuL < pL . The firm offering wH
H
H
e
e
e
u
workers will then offer wL = w
ˆ (wH ) = wL + ε to low-ability workers. Since wuH > wuL , firms offering
these wages separate workers hired from unemployment and employment. Let Nie (w) denote the mass
of workers hired from employment with ability i earning a wage no greater than
P w. The steady-state
profit from hiring employed workers at these wages is given by Ωe (wuH , wuL ) = i=L,H Ωei (wui ), where
Ωei (wui ) =
=
λ[Niu (wui ) + Nie (wui )](pi − wui )
φ + δ + ρ + λ(1 − Fie (wui ))
λFiu (wui )Ωui (wui )
λNie (wui )(pi − wui )
+
.
φ + δ + ρ + λ(1 − Fie (wui )) φ + δ + ρ + λ(1 − Fie (wui ))
55
(61)
P
P
Since in equilibrium i=L,H Ωui (Ri ) = i=L,H Ωui (wui ), comparing the profits from offering (weH , weL )
and (wuH , wuL ) to employed workers implies Ωe (wuH , wuL ) > Ωe (weH , weL ), contradicting the constant profit
condition on the employed workers’ market.
e = wu + ε ≤ p
Now suppose that offering a wage wH
H to unemployed workers of high ability imH
u >p .
plies that satisfying the incentive-compatibility constraint of low-ability workers yields a wage wL
L
u
In this case the firms will offer pooling contracts with initial wage wH to both unemployed and emu
u
ployed
workers. Noting
that in equilibrium
P
P thatuwe ucan still use (61), with wei =uwH ufor i =e L, eH and
e ), once again contrau
w
),
one
can
verify
that
Ω
(w
,
)
>
Ω
(w
,
w
Ω
(R
)
=
Ω
(w
i
i=L,H i
i=L,H i
H
H
L
H
L
dicting the constant-profit condition on the employed workers’ market.
Finally, assume that the incentive constraint of low-ability workers is slack at wages wui for i = L, H.
In this case, we could have that incentive compatibility implies wuH < wuL and firms offering wuH to
unemployed workers of high ability can decide to pool workers, while the firm offering wuH to employed
workers of high ability decides to separate. Note, however, that when the incentive constraint is slack,
the constant-profit condition can be applied to high-ability workers independently in both the employed
and unemployed workers’ market. Hence using ΩuH (RH ) = ΩuH (wuH ) and (60) and (61), we obtain
that ΩeH (RH ) < ΩeH (wuH ), which contradicts the constant-profit condition on the market for employed
high-ability workers.
Taking the above arguments together, they show that in any equilibrium wei > wui for all i = L, H.
2
An implication of Lemma 4 is that all firms offer unemployed workers the separating pair of reservation initial wages (RH , RL ), while employed workers are offered initial wages wi > Ri , drawn from cdf
Fi , such that the infimum of the support of Fi is equal to Ri . We now proceed to characterize separating
and pooling equilibria for this economy.
General considerations
Since firms offer unemployed workers their reservation wage, unemployment utility for both types is
identical, satisfying UL = UH = U = b/φ . Bellman equations for (truthful and misreporting) low-ability
workers and for (truth-telling) high-ability workers are
Z
[φ + δ + ρ + λ]VLL (w) = w + δU + ρVL (pL ) + λ max[VLL (w(w
ˆ 0 )), VLH (w0 ), VLL (w)]dFH (w0 ) ,
Z
[φ + δ + ρ + λ]VLH (w) = w + [δ + ρ]U + λ max[VLL (w(w
ˆ 0 )), VLH (w0 ), VLH (w)]dFH (w0 ) ,
Z
[φ + δ + ρ + λ]VHH (w) = w + δU + ρVH (pH ) + λ max[VHL (w(w
ˆ 0 )), VHH (w0 ), VHH (w)]dFH (w0 ) .
From Vii (Ri ) = U follow the reservation wage equations
Z
Ri = b − ρ[Vi (pi ) − U ] − λ max[ViL (w(w)),
ˆ
ViH (w)] − U dFH (w) .
Since promoted high-ability workers do not quit, it follows that ρ[VH (pH ) − U ] =
(62)
ρ(pH − b)
. Further
φ+δ
define x ≡ ρ[VL (pL ) − U ]. Then the incentive constraint for low-ability workers is
wH − wL ≤ x .
56
(63)
Separating equilibrium
Since all firms offer separating contracts with initial wages wL ≤ pL , promoted low-ability workers
do not quit. Therefore,
ρ(pL − b)
x=
.
(64)
φ+δ
Since no low-ability worker misreports the type, unemployment rates for both types are identical,
uL = uH = u =
(φ + δ)
.
φ+δ+λ
Let hi denote the fraction of employed workers of type i hired from unemployment and earning initial
reservation wage Ri . Further, let Gi (w) denote the cumulative distribution of initial wages for workers
hired from another employer. In steady state this distribution satisfies
Gi (w) =
λhi Fi (w)
.
φ + δ + ρ + λ(1 − Fi (w))
The steady-state workforce of workers of ability i employed at initial wage wi is
`i (wi ) =
λαi (1 − u)(hi + Gi (wi ))
.
φ + δ + ρ + λ(1 − Fi (wi ))
It follows that firms’ profits are again given by (7), with a redefinition of parameter A0 ≡ λ2 (φ + δ)/(φ +
δ + λ). It follows that the wage-offer distribution for wi ≤ w
˜i is again given by (8). For wages above
w
˜i , the binding incentive constraint (63) and ΩH (wH ) + ΩL (wH − x) = ΩH (RH ) + ΩL (RL ) yield the
wage-offer distribution
"
#
(φ + δ + ρ + λ)
p − wH (1 + α) + αx 1/2
FH (wH ) =
1−
, wH ≥ w
˜H ,
λ
p−R
where p and R are defined as in the main text.
We again consider a rank-preserving equilibrium. From (10) follows that the incentive constraint
(63) is slack for wages
(p − RH )x + pH RL − pL RH
,
(65)
wH ≤ w
˜H ≡ H p −
RH − pL + RL
H
while for wages above w
˜H , wL = w(w
ˆ H ) = wH − x.
To characterize an equilibrium with slack incentive constraints and to derive threshold parameter
ρ1 , note that
Z wi
Z wi
λ(1 − Fi (w))
λ
dw = (pi − Ri )(1 + C 2 − 2C) ,
[Vii (w) − Vii (Ri )]dFi (w) =
φ
+
δ
+
ρ
+
λ(1
−
F
(w))
i
Ri
Ri
with parameter C defined as in (12). Reservation wages can then be obtained from (62) and (64):
Ri = pi − (pi − b)
φ+δ+ρ
.
(φ + δ)C(2 − C)
(66)
Since promotion wages for high-ability workers are higher, we have RH < RL . Incentive constraints
are slack if wH − wL ≤ x, where top initial wages wi are related to reservation wages via (12). Hence,
threshold parameter ρ1 is the implicit solution of
pH − pL − C 2 (pH − pL − RH + RL ) = x ,
57
with reservation wages (66).
If ρ ≤ ρ1 , incentive constraints bind at the top of the wage offer distribution. A separating equilibrium with this feature is similarly characterized as in the main text. Instead of (17) we have
i
h
2
1
wH = 1 +
p
+
αx
−
C
(p
−
R)
, wL = wH − x .
α
This outcome only describes a separating equilibrium if wL does not exceed marginal productivity of
low-ability workers. Hence, the threshold value ρ2 is defined as the highest value for which wH − x = pL
and hence ensures that a separating equilibrium exists for all ρ ≥ ρ2 .
In a separating equilibrium with binding incentive constraints, reservation wages for the two worker
λ(1−Fi (w))
types can be similarly calculated as in the proof of Proposition 1. Define again hi (w) ≡ φ+δ+ρ+λ(1−F
,
i (w))
and write (62) as
Z wi
ρ
Ri − b +
(p − b) =
hi (w)dw .
φ+δ i
R
i
As in the proof of Proposition 1, these integrals can be calculated as follows:
Z wH
i
1 h
hH (w)dw =
(p − R)(1 + C 2 ) + α(x + RL − RH )
1+α
RH
+2C
1
[pH − pL − x]1/2 [pH − RH − pL + RL ]1/2 − 2C(pH − RH ) ,
1+α
Z wL
i
1 h
hL (w)dw =
(p − R)(1 + C 2 ) + RH − RL − x
1+α
RL
1
[pH − pL − x]1/2 [pH − RH − pL + RL ]1/2 − 2C(pL − RL ) .
1+α
Adding the equation for RH to the one for RL multiplied by α, the resulting equation can be solved for
R = RH + αRL :
φ+δ+ρ
.
R = p − [p − (1 + α)b]
(φ + δ)C(2 − C)
−2C
Substitution of RH = R − αRL into the reservation wage equation for RL yields a quadratic equation
in RL whose relevant root is
p
−D
+
D2 − 4E
RL =
2
with
h
i
2
1
N ≡ x − b − 2CpL + 1 +
(p
−
R)(1
+
C
)
+
R
−
x
,
α
1
D≡N
C − 1 + α (pH − pL − x) ,
2
1
E≡ N2−
(pH − pL − R)(pH − pL − x) .
4C
(1 + α)2
These reservation wages together with the previous equations for w
˜i , wH , wL = wH − x, and the wage
offer distributions characterize the separating equilibrium with binding incentive constraints.
Segmented equilibrium with pooling at top wages
As in the main text, a pooling equilibrium is characterized by the variables (ϕ, ξ, η, RL , RH ). All
firms offer separating initial wages (RH , RL ) to unemployed workers and dispersed initial wages to
employed workers. Fraction ϕ > 0 of firms offer separating contracts (wH , wL ) with wL < pL , fraction
58
η > 0 offer the same separating contract (pL + x, pL ), and fraction 1 − ϕ − η ≥ 0 offer dispersed pooling
contracts (wH ) with wH > pL + x. Low-ability workers who are employed at initial wage wL < pL and
quit to a firm offering (pL + x, pL ) misreport their type with probability ξ > 0. One possibility is that
the mass point at wH = pL + x is the highest offered contract; this happens when the learning rate is
sufficiently large (greater than some threshold ρ3 < ρ2 ). The other possibility, when ρ < ρ3 , is that
positive mass of firms offer pooling contracts with wH > pL + x.
To obtain steady-state measures, write Gi (w) for the earnings distribution of initial wages for those
workers who were hired from another employer. Write hi for the measure of workers who were hired
from unemployment and currently earn initial wage Ri , and write gi∗ (pi ), i = H, L, for the measures of
∗ , p ),
employed workers after promotion. Since the distribution of initial wages has a mass point at (wH
L
∗
∗
∗
we write gL (pL ), gL (wH ) and gH (wH ) for the measures of workers earning pL (low ability) or wH (high
and low ability) before promotion/layoff. These earnings distribution depend on equilibrium variables
(ϕ, ξ, η, RL , RH ) as follows.
∗ )−
Low-ability workers: Write g1 = GL− (pL ), g2 = GL (pL ) − GL− (pL ) = gL (pL ), g3 = GL (wH
∗
∗
∗
∗
GL− (wH ) = gL (wH ), g4 = GL (wH ) − GL (wH ), g6 = g (pL ). Thus, fraction G0 ≡ g1 + g2 + g3 + g4 of
employed low-ability workers receive initial wages and were hired from another employer. Fraction g6
have been promoted, and hL were hired from unemployment. Hence, G0 + g6 + hL = 1. Mass αL uL
∗ ) =
of workers is unemployed and mass αL (1 − uL ) is employed. As in the benchmark model, GL− (wH
∗
GL (pL ) because no low-ability worker earns a wage in the interval (pL , wH ). G0 , g1 , g2 , g3 , g6 , hL and
uL satisfy the following steady-state equations
g1 [φ + δ + ρ + λ(1 − ϕ)] = hL λϕ ,
g2 [φ + δ + ρ + λ(1 − ϕ − η)] = (hL + g1 )λ(1 − ξ)η ,
g3 [φ + δ + ρ + λ(1 − ϕ − η)] = (hL + g1 )λξη ,
G0 [φ + δ + ρ] = hL λ + λg6 (1 − η − ϕ) ,
g6 [φ + δ + λ(1 − ϕ − η)] = ρ(hL + g1 + g2 ) ,
(1 − uL )hL [φ + δ + ρ + λ] = uL λ ,
uL [φ + λ] = φ + (1 − uL )δ + (1 − uL )(g3 + g4 )ρ .
We can solve these as follows:
g1 =
g2 =
g3 =
g6 =
hL =
uL =
λϕ
h ≡ AhL ,
φ + δ + ρ + λ(1 − ϕ) L
(1 + A)λ(1 − ξ)η
h ≡ BhL ,
φ + δ + ρ + λ(1 − ϕ − η) L
(1 + A)λξη
h ,
φ + δ + ρ + λ(1 − ϕ − η) L
(1 + A + B)ρ
h ≡ DhL ,
φ + δ + λ(1 − ϕ − η) L
φ+δ+ρ
,
λ + φ + δ + ρ + D(φ + δ + ρ + λ(1 − η − ϕ))
(φ + δ + ρ + λ)hL
.
λ + hL (φ + δ + ρ + λ)
The stationary earnings distribution of initial wages is
λhL FL (w)
φ + δ + ρ + λ(1 − FL (w))
λhL FH (w) + λg6 (FH (w) − ϕ − η)
GL (w) =
φ + δ + ρ + λ(1 − FH (w))
GL (w) =
59
if
w < pL ,
if
∗
w > wH
.
High-ability workers: Here the same equations for GH as in the proof of Proposition 2 apply.
The unemployment rate is uH = (φ + δ)/(φ + δ + λ), and mass hH = uH λ/(1 − uH )/(φ + δ + ρ + λ) of
employed workers were hired from unemployment and earn initial wage RH .
Profit Maximization: To find wage-offer distributions from the firms’ profit-maximization conditions, define α
ˆ ≡ αuL /uH as the measure of low-ability unemployed workers per unemployed high-ability
worker. Hence, a random worker hired from unemployment has high ability with probability 1/(1 + α
ˆ)
and low ability otherwise. Further define parameter A0 as above.
Wage-offer distributions in the four possible cases are similar to those in the proof of Proposition 2
with the following differences:
wH ∈ [RH , w
˜H ): Separating contracts with slack incentive constraints. Here the wage offer
distributions are again given by (8), and the threshold wage w
˜H is given by (65).
∗
wH ∈ [w
˜H , wH ): Separating contracts with binding incentive constraints. With binding
incentive constraints wL = wH − x, the firms’ profit is
h
i
A0
Ω(wH , wH − x) =
p
−
w
+
α
ˆ
(p
−
w
+
x)
.
H
H
L
H
(φ + δ + ρ + λ(1 − FH (wH )))2
The constant profit condition Ω(wH , wH − x) = Ω(RH , RL ) yields the same wage offer distribution
ˆ ≡ RH + α
as in (44), where the term (b − RL ) is replaced by x, and pˆ ≡ pH + α
ˆ pL and R
ˆ RL are
similarly defined. With the same definition of C(x) as in the proof of Proposition 2, the restriction
∗ )=F
FH− (wH
L− (pL ) = ϕ implies the equilibrium condition for ϕ:
C(ϕ)2 =
pH − pL − x
.
ˆ
pˆ − R
(67)
∗ with some pooling and layoffs of low-ability workers. Fraction
Mass point at wH = wH
ξ of low-ability workers misreport their type while the rest accept pL . On each misreporting worker of
∗ the firm makes expected (negative) profit
low ability hired at wH
∗
JL (wH
)=−
x
.
φ + δ + ρ + λ(1 − ϕ − η)
The rate at which low-ability workers are hired into this contract is
h
i
∗
hL (wH
) = αλξ(1 − uL ) hL + GL− (pL ) =
λ2 α
ˆ ξ(φ + δ)
.
(φ + δ + λ)[φ + δ + ρ + λ(1 − ϕ)]
∗ is
Therefore the firm’s profit on low-ability workers at wage wH
∗
∗
∗
ΩL (wH
) = hL (wH
)JL (wH
)=−
A0 α
ˆ ξx
.
[φ + δ + ρ + λ(1 − ϕ)][φ + δ + ρ + λ(1 − ϕ − η)]
∗ ) is the same as in the proof of Proposition 2. The constantFirms’ profits on high-ability workers ΩH (wH
∗ ) + Ω (w ∗ ) = Ω(R , R ) then implies the equilibrium condition for variable
profit condition ΩL (wH
H
H
L
H
ξ:
pH − pL − x − ξ α
ˆx
C(ϕ)C(ϕ + η) =
.
(68)
ˆ
pˆ − R
∗ : Pooling contracts with layoffs of low-ability workers.
wH > wH
This is only an equilibrium strategy if 1 − ϕ − η > 0. Otherwise (i.e. 1 − ϕ − η = 0), the highest
∗ . Each worker of low ability hired at w > w ∗ yields (negative) profit
initial wage is at wH
H
H
JL (wH ) =
p L − wH
.
φ + δ + ρ + λ(1 − FH (wH ))
60
The rate at which low-ability workers are hired into this contract is
h
i
(φ + δ + ρ + λ)(hL + g6 ) − λg6 (ϕ + η)
hL (wH ) = λα(1 − uL ) hL + GL (wH ) + g6 = λα(1 − uL )
.
φ + δ + ρ + λ(1 − FH (w))
With the redefinition
[(φ + δ + ρ + λ)(hL + g6 ) − λg6 (ϕ + η)](φ + δ + λ)
ˆ
α
ˆ ≡ α(1 − uL )
,
λ(φ + δ)
∗ is
the firm’s expected (negative) profit on low-ability workers at wages wH > wH
ΩL (wH ) = hL (wH )JL (wH ) =
ˆˆ (pL − wH )
A0 α
.
[φ + δ + ρ + λ(1 − FH (wH ))]2
Profit on high-ability workers ΩH (wH ) is the same as in the proof of Proposition 2. Then the constantprofit condition ΩL (wH ) + ΩH (wH ) = Ω(RH , RL ) yields the wage offer distribution

!1/2 
ˆ
ˆ
φ+δ+ρ+λ
pˆ − wH (1 + α
ˆ)
∗
 , wH ∈ (wH
FH (wH ) =
1−
, wH ] ,
ˆ
λ
pˆ − R
ˆ
where pˆˆ ≡ pH + α
ˆ pL . The top wage follows from FH (wH ) = 1:
wH =
1
ˆ
1+α
ˆ
h
pˆˆ −
i
φ + δ + ρ 2
ˆ .
(ˆ
p − R)
φ+δ+ρ+λ
∗ ) = lim
∗ FH (wH ) = ϕ + η follows the condition for variable
From the limiting condition FH+ (wH
wH &wH
η (provided that η < 1 − ϕ):
ˆˆ x
pH − pL − x − α
C(ϕ + η)2 =
.
(69)
ˆ
pˆ − R
Reservation Wages
We first calculate the value VL (pL ):
Z
(φ + δ)VL (pL ) = pL + δU + λ
Z
= pL + δU +
wH
∗
wH
wH
∗
wH
[VLH (w) − VL (pL )] dFH (w) ,
λ(1 − FH (w))
dw .
φ + δ + ρ + λ(1 − FH (w))
(70)
The last integral is
Z wH
Z wH 1/2
ˆ
λ(1 − FH (w))
φ+δ+ρ
pˆ − R
∗
dw = wH − wH
−
dw
φ + δ + ρ + λ w∗
ˆˆ )w
pˆˆ − (1 + α
w∗ φ + δ + ρ + λ(1 − FH (w))
H
H
∗
= w H − wH
−2
C(1)[C(ϕ + η) − C(1)]
ˆ .
(ˆ
p − R)
ˆˆ
1+α
∗ = p + x can be used to obtain x:
This equation together with (70), x = ρ[VL (p) − U ] and wH
L
x=
n
o
C(1)[C(ϕ + η) − C(1)]
ρ
ˆ .
wH − b − 2
(ˆ
p − R)
φ+δ+ρ
ˆˆ
1+α
61
(71)
The reservation wage for low-ability workers satisfies
Z wH
RL = b − x − λ
max[VLL (w(w)),
ˆ
VLH (w)] − U dFH (w) .
(72)
RH
The integral is
"Z
pL
λ
Z
VLL (w)−U dFL (w)+η[VL (pL )−U ]+
RL
Z
pL
=
RL
wH
∗
wH
#
∗
VLH (w)−VLH (wH
)dFH (w)+(1−ϕ−η)[VL (pL )−U ]
λ(1 − FL (w))
λ(1 − ϕ)x (φ + δ)x
+
+ b − pL
dw +
ρ
ρ
φ + δ + ρ + λ(1 − FL (w))
= (pL − RL )(1 − 2C(ϕ)) +
2C(ϕ)2
ˆ − 2C(ϕ) (pH − RH − pL + RL )1/2 (pH − pL − x)1/2
(ˆ
p − R)
1+α
ˆ
1+α
ˆ
(λ(1 − ϕ) + φ + δ)x
+ b − pL .
ρ
Here the last equation makes use of the same integral formula as in the proof of Proposition 2. Substitution of this expression and (71) into (72) gives the reservation-wage equation for RL .
Regarding the reservation-wage equation for RH , we can also make use of the integral formula in
the proof of Proposition 2, which gives
Z wH
ρ
b − RH −
(p − b) = λ
VHH (w) − VHH (RH )dFH (w) =
(73)
φ+δ H
R
+
H
wH − RH − 2C(1)(pH − RH ) +
+
2C(1)C(ϕ)
ˆ
(ˆ
p − R)
1+α
ˆ
2C(1)α
ˆ
2C(1)[C(1) − C(ϕ + η)]
ˆ .
(ˆ
p − R)
(p − pL − RH + RL )1/2 (pH − pL − x)1/2 +
ˆˆ
1+α
ˆ H
1+α
The equilibrium variables (ϕ, ξ, η, RL , RH ) are determined by the five equations (67), (68), (69), (72)
and (73), when η + ϕ < 1. Otherwise, equation η + ϕ = 1 replaces (69).
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